Well, in case this helps anyone else out, I made a quick and (very) dirty change to class-piklist-form.php. This change is to account for my two taxonomies, the first one ‘issues’ that is a multi select checkbox list and the second ‘locations’ which is a simple single select dropdown.

Around line 3292, just after
self::$form_submission = $fields_data;

I added the following (customize for your taxonomies and list types):

$formobjID = $fields_data['post']['post_type']['object_id']; //gets the object ID from the form data
$issues = $fields_data['taxonomy']['my_issues']['request_value']; // gets my issue array submitted
$issueIDS = array_map('intval', $issues); //converts to int, because they are strings when submitted for some reason

$locations = $fields_data['taxonomy']['my_locations']['request_value'];
$locationsIDS = intval($locations);

wp_set_object_terms( $formobjID,$issueIDS, 'my_issues' );  
wp_set_object_terms( $formobjID, $locationsIDS, 'my_locations' ); 

I am having this same issue, taxonomy items from front end are not saving. Is there a workaround or bugfix somewhere?

Sure here it is just slightly simplified:

<?php
/*
Title: my-component Fields
Post Type: my-component
Order: 10
*/
  

  
piklist('field', array(
    'type' => 'datepicker'
    ,'field' => 'expiration_date'
    ,'required' => true
    ,'label' => __('Expiration Date', 'my-component')
    ,'description' => __('Choose an expiration date', 'my-component')
    ,'options' => array(
      'dateFormat' => 'yy-mm-dd'
    )
    ,'attributes' => array(
      'size' => 17
    )
    ,'on_post_status' => array(
      'value' => 'lock'
    )
  ));   
piklist('field', array(
 'type' => 'textarea'
   ,'field' => 'my_brief_description'
   ,'label' => __('Brief Description', 'my-component')
,'description' => 'Type your brief description here. It will show up in lists.'
   //,'value' => ''
    ,'attributes' => array(
      'rows' => 5
      ,'cols' => 50
      ,'class' => 'large-text'
    )
  ));  
  

 piklist('field', array(
    'type' => 'editor'
    ,'field' => 'post_content'
    ,'scope' => 'post'
    ,'required' => false
    ,'label' => __('Full Description', 'my-component')
    ,'description' => __('Type your long description here. It will show up on the detail page.', 'my-component')
   // ,'value' => ''
    ,'options' => array(
      'wpautop' => true
      ,'media_buttons' => false
      ,'shortcode_buttons' => false
      ,'teeny' => false
      ,'dfw' => false
      ,'tinymce' => array(
        'resize' => false
        ,'wp_autoresize_on' => true
      )
      ,'quicktags' => true
      ,'drag_drop_upload' => false
    )
    ,'on_post_status' => array(
      'value' => 'lock'
    )
  ));

piklist('field', array(
    'type' => 'group'
    ,'label' => __('Things to do', 'my-component')
    ,'add_more' => true
    ,'description' => __('List all the things', 'my-component')
    ,'fields' => array(
    array(
    'type' => 'select'
    ,'field' => 'typeofthing'
    ,'label' => __('type of thing', 'my-component')
    ,'value' => 'none'
    ,'required' => true
    ,'choices' => array(
		'' => 'Choose thing'      
	  ,'thing' => __('thing', 'my-component')
      ,'thing_two' => __('2', 'my-component')
      ,'thing_three' => __('3', 'my-component')
      ,'thing_four' => __('4', 'my-component')
      ,'thing_five' => __('5', 'my-component')
      ,'thing_six' => __('6', 'my-component')
      ,'thing_seven' => __('7', 'my-component')
      ,'thing_eight' => __('8', 'my-component')
      ,'thing_nine' => __('9', 'my-component')
      ,'thing_ten' => __('10', 'my-component')
      ,'thing_eleven' => __('11', 'my-component')
      //,'thing_twelve' => __('12', 'my-component')
    ))
// thing FIELDS
     ,array(
        'type' => 'text'
        ,'field' => 'thing_phonenumber'
        ,'label' => __('Phone Number', 'my-component')
        ,'columns' => 12
            ,'conditions' => array(
      array(
        'field' => 'typeofthing'
        ,'value' => 'thing'
      )
    )
      )
 	 ,array(
        'type' => 'text'
        ,'field' => 'thing_who'
        ,'label' => __('Who to call?', 'my-component')
        ,'columns' => 12
            ,'conditions' => array(
      array(
        'field' => 'typeofthing'
        ,'value' => 'thing'
      )
    )
      )
    	 ,array(
        'type' => 'editor'
        ,'field' => 'thing_notes'
        ,'label' => __('Notes', 'my-component')
        ,'columns' => 12
            ,'conditions' => array(
      array(
        'field' => 'typeofthing'
        ,'value' => 'thing'
      )
    )
      ) 
      
// thing_two fields
 	,array(
        'type' => 'select'
        ,'field' => 'thing_two_lookup'
        ,'label' => __('thing_two_lookup', 'my-component')
    	,'value' => 'none'
    	,'choices' => thing_two_lookup_choices()
    	,'attributes' => array(
      'multiple' => 'multiple' // Allow a select field to accept multiple selections
    	)        
    	,'columns' => 12
        ,'conditions' => array(
      array(
        'field' => 'typeofthing'
        ,'value' => 'thing_two'
      )
    )
      )
      ,array(
        'type' => 'select'
        ,'field' => 'thing_two_lookup_second'
        ,'label' => __('thing_two_lookup_second', 'my-component')
    	,'value' => 'none'
    	,'choices' => thing_two_lookup_choices_second()
    	,'attributes' => array(
      'multiple' => 'multiple' // Allow a select field to accept multiple selections
    	)        
    	,'columns' => 12
        ,'conditions' => array(
      array(
        'field' => 'typeofthing'
        ,'value' => 'thing_two'
      )
    )
      )                        
   ,array(
        'type' => 'editor'
        ,'field' => 'thing_two_notes'
        ,'label' => __('Notes', 'my-component')
        ,'columns' => 12
            ,'conditions' => array(
      array(
        'field' => 'typeofthing'
        ,'value' => 'thing_two'
      )
    )
      )         

// thing_three FIELDS
 	,array(
        'type' => 'text'
        ,'field' => 'thing_three_who'
        ,'label' => __('thing_three who', 'my-component')
        ,'columns' => 12
            ,'conditions' => array(
      array(
        'field' => 'typeofthing'
        ,'value' => 'thing_three'
      )
    )
      )
 	,array(
        'type' => 'text'
        ,'field' => 'thing_three_address'
        ,'label' => __('thing_three Address', 'my-component')
        ,'columns' => 12
            ,'conditions' => array(
      array(
        'field' => 'typeofthing'
        ,'value' => 'thing_three'
      )
    )
      )  	
      ,array(
        'type' => 'text'
        ,'field' => 'thing_three_subject'
        ,'label' => __('thing_three Subject', 'my-component')
        ,'columns' => 12
            ,'conditions' => array(
      array(
        'field' => 'typeofthing'
        ,'value' => 'thing_three'
      )
    )
      ) 
 	,array(
        'type' => 'editor'
        ,'field' => 'thing_three_template'
        ,'label' => __('thing_three template', 'my-component')
        ,'columns' => 12
            ,'conditions' => array(
      array(
        'field' => 'typeofthing'
        ,'value' => 'thing_three'
      )
    )
      )     
   
// thing_four FIELDS
     ,array(
        'type' => 'text'
        ,'field' => 'thing_four_url'
        ,'label' => __('URL of thing_four', 'my-component')
        ,'columns' => 12
            ,'conditions' => array(
      array(
        'field' => 'typeofthing'
        ,'value' => 'thing_four'
      )
    )
      )    
       
// thing_five FIELDS   
      ,array(
        'type' => 'text'
        ,'field' => 'thing_five_who'
        ,'label' => __('thing_five Addresee', 'my-component')
        ,'columns' => 12
            ,'conditions' => array(
      array(
        'field' => 'typeofthing'
        ,'value' => 'thing_five'
      )
    )
      ) 
      ,array(
        'type' => 'text'
        ,'field' => 'thing_five_address'
        ,'label' => __('thing_five Address', 'my-component')
        ,'columns' => 12
            ,'conditions' => array(
      array(
        'field' => 'typeofthing'
        ,'value' => 'thing_five'
      )
    )
      )
      ,array(
        'type' => 'text'
        ,'field' => 'thing_five_address_2'
        ,'label' => __('thing_five 2', 'my-component')
        ,'columns' => 12
        ,'conditions' => array(
      array(
        'field' => 'typeofthing'
        ,'value' => 'thing_five'
      )
    )
      )
      ,array(
        'type' => 'text'
        ,'field' => 'send_letter_city'
        ,'label' => __('City', 'my-component')
        ,'columns' => 5
        ,'conditions' => array(
      array(
        'field' => 'typeofthing'
        ,'value' => 'thing_five'
      )
    )      )
      ,array(
        'type' => 'select'
        ,'field' => 'thing_five_state'
        ,'label' => __('thing_five State', 'my-component')
        ,'columns' => 4
        ,'choices' => piklist_get_states()
        ,'conditions' => array(
      array(
        'field' => 'typeofthing'
        ,'value' => 'thing_five'
      )
    )
      )
      ,array(
        'type' => 'text'
        ,'field' => 'thing_five_postal_code'
        ,'label' => __('thing_five Postcode', 'my-component')
        ,'columns' => 3
        ,'conditions' => array(
      array(
        'field' => 'typeofthing'
        ,'value' => 'thing_five'
      )
    )        
      )
            
//thing_six FIELDS
     ,array(
        'type' => 'text'
        ,'field' => 'thing_six_url'
        ,'label' => __('URL of thing_six', 'my-component')
        ,'columns' => 12
            ,'conditions' => array(
      array(
        'field' => 'typeofthing'
        ,'value' => 'thing_six'
      )
    )
      ) 
      
// thing_seven FIELDS
    ,array(
        'type' => 'text'
        ,'field' => 'thing_seven_where'
        ,'label' => __('thing_seven where', 'my-component')
        ,'columns' => 12
            ,'conditions' => array(
      array(
        'field' => 'typeofthing'
        ,'value' => 'thing_seven'
      )
    )
      )  
,array(
        'type' => 'text'
        ,'field' => 'thing_seven_datetime'
        ,'label' => __('thing_seven time', 'my-component')
    	,'attributes' => array(
     	 'class' => 'dtpicker'
   		 )        
   	 ,'columns' => 12
    ,'conditions' => array(
      array(
        'field' => 'typeofthing'
        ,'value' => 'thing_seven'
      )
    )
      )
      ,array(
        'type' => 'text'
        ,'field' => 'thing_seven_datetime_end'
        ,'label' => __('thing_seven end', 'my-component')
    	,'attributes' => array(
     	 'class' => 'dtpicker'
   		 )        
   	 ,'columns' => 12
    ,'conditions' => array(
      array(
        'field' => 'typeofthing'
        ,'value' => 'thing_seven'
      )
    )
      )        
    ,array(
        'type' => 'text'
        ,'field' => 'thing_seven_url'
        ,'label' => __('URL thing_seven', 'my-component')
        ,'columns' => 12
            ,'conditions' => array(
      array(
        'field' => 'typeofthing'
        ,'value' => 'thing_seven'
      )
    )
      ) 

// thing_eight FIELDS
    ,array(
        'type' => 'text'
        ,'field' => 'thing_eight_where'
        ,'label' => __('Where thing_eight', 'my-component')
        ,'columns' => 12
            ,'conditions' => array(
      array(
        'field' => 'typeofthing'
        ,'value' => 'thing_eight'
      )
    )
      )  
 
,array(
        'type' => 'text'
        ,'field' => 'thing_eight_datetime'
        ,'label' => __('thing_eight time', 'my-component')
    	,'attributes' => array(
     	 'class' => 'dtpicker'
   		 )        
   	 ,'columns' => 12
    ,'conditions' => array(
      array(
        'field' => 'typeofthing'
        ,'value' => 'thing_eight'
      )
    )
      )
      ,array(
        'type' => 'text'
        ,'field' => 'thing_eight_datetime_end'
        ,'label' => __('thing_eight end', 'my-component')
    	,'attributes' => array(
     	 'class' => 'dtpicker'
   		 )        
   	 ,'columns' => 12
    ,'conditions' => array(
      array(
        'field' => 'typeofthing'
        ,'value' => 'thing_eight'
      )
    )
      )        
    ,array(
        'type' => 'text'
        ,'field' => 'thing_eight_url'
        ,'label' => __('URL thing_eight', 'my-component')
        ,'columns' => 12
            ,'conditions' => array(
      array(
        'field' => 'typeofthing'
        ,'value' => 'thing_eight'
      )
    )
      ) 
              
// thing_nine FIELDS
    ,array(
        'type' => 'text'
        ,'field' => 'thing_nine_where'
        ,'label' => __('Where thing_nine', 'my-component')
        ,'columns' => 12
            ,'conditions' => array(
      array(
        'field' => 'typeofthing'
        ,'value' => 'thing_nine'
      )
    )
      )  
,array(
        'type' => 'text'
        ,'field' => 'thing_nine_datetime'
        ,'label' => __('thing_nine time', 'my-component')
    	,'attributes' => array(
     	 'class' => 'dtpicker'
   		 )        
   	 ,'columns' => 12
    ,'conditions' => array(
      array(
        'field' => 'typeofthing'
        ,'value' => 'thing_nine'
      )
    )
      )
      ,array(
        'type' => 'text'
        ,'field' => 'thing_nine_datetime_end'
        ,'label' => __('thing_nine end', 'my-component')
    	,'attributes' => array(
     	 'class' => 'dtpicker'
   		 )        
   	 ,'columns' => 12
    ,'conditions' => array(
      array(
        'field' => 'typeofthing'
        ,'value' => 'thing_nine'
      )
    )
      )        
          ,array(
        'type' => 'text'
        ,'field' => 'thing_nine_url'
        ,'label' => __('URL thing_nine', 'my-component')
        ,'columns' => 12
            ,'conditions' => array(
      array(
        'field' => 'typeofthing'
        ,'value' => 'thing_nine'
      )
    )
      )
             
// thing_ten FIELDS   
      ,array(
        'type' => 'text'
        ,'field' => 'thing_ten_who'
        ,'label' => __('thing_ten who', 'my-component')
        ,'columns' => 12
            ,'conditions' => array(
      array(
        'field' => 'typeofthing'
        ,'value' => 'thing_ten'
      )
    )
      ) 
      ,array(
        'type' => 'text'
        ,'field' => 'thing_ten_url'
        ,'label' => __('URL thing_ten', 'my-component')
        ,'columns' => 12
            ,'conditions' => array(
      array(
        'field' => 'typeofthing'
        ,'value' => 'thing_ten'
      )
    )
      )
                       
// thing_eleven  FIELDS
     ,array(
        'type' => 'text'
        ,'field' => 'thing_eleven_url'
        ,'label' => __('URL thing_eleven', 'my-component')
        ,'columns' => 12
            ,'conditions' => array(
      array(
        'field' => 'typeofthing'
        ,'value' => 'thing_eleven'
      )
    )
      )
   

    )
    ,'on_post_status' => array(
        'value' => 'lock'
      )
  ));
  

I should add that even after consolidating several of the types above (for example, all of those that just had a url field into a typename/url combo, I only saw a very small performance benefit of a second or two off the 8 second add.

It occurs to me that I am having this exact same problem (reported here). I suppose one solution would be to try to structure the data differently so fields are reused (reducing the total number and thus improving performance). Is this completely a JS rendering problem that has no piklist solution?

Nevermind I figured it out. Here is the code if it helps someone:

In my setup plugin:

// DATETIMEPICKER ENQUEUE

add_filter('piklist_assets', 'my_assets');

function my_assets($assets)
{
  array_push($assets['scripts'], array(
    'handle' => 'datetimepicker'
    ,'src' => get_template_directory_uri() . '/js/jquery.datetimepicker.full.js'
    ,'ver' => '2.5.4'
    ,'deps' => 'jquery'
    ,'enqueue' => true
    ,'in_footer' => true
    ,'admin' => true
    ,'front' => false
  ));

 array_push($assets['scripts'], array(
    'handle' => 'dtpickermine'
    ,'src' => get_template_directory_uri() . '/js/dtpickermine.js' //my jQuery(document).ready code...
    ,'ver' => '1.0'
    ,'deps' => 'jquery'
    ,'enqueue' => true
    ,'in_footer' => true
    ,'admin' => true
    ,'front' => false
  ));

  array_push($assets['styles'], array(
    'handle' => 'datetimepickerclasses'
    ,'src' => get_template_directory_uri() . '/js/jquery.datetimepicker.css'
    ,'ver' => '1.2'
    ,'enqueue' => true
    ,'in_footer' => true
    ,'admin' => true
    ,'media' => 'screen, projection'
  ));
  
  return $assets;
}  

And then in my meta field definition:

piklist('field', array(
 'type' => 'text'
   ,'field' => 'ae_dtpicker'
   ,'label' => __('my date time', 'direct-action')
    ,'attributes' => array(
      'class' => 'dtpicker'
    )
  ));    

Anything at all?