no, message is still there

thanks Steve,

nailed it.
i made a function to retrieve the posts and moved the code below to the function inside the plugin file

$args = array(
	'post_type' => 'tour',
	'tax_query' => array(
		array(
			'taxonomy' => 'traka_taxo',
			'field'    => 'slug',
			'terms'    => 'best-of',
		),
	),
);

$best_of_choices = array();
$query = new WP_Query( $args );

if ( $query->have_posts() ) {
	while ( $query->have_posts() ) : $query->the_post(); 
		$best_of_choices[] = array("post_id" => get_the_ID(), "post_name" => get_the_title()); 
	endwhile; 
	wp_reset_postdata();
} else { 
	_e( 'Sorry, no posts matched your criteria.' ); 
}

but still it did not save.

then i decided to go back to the defaults, removing
'choices' => piklist($best_of_choices, array('post_id','post_name'))

and use

'choices' => array(
'one' => 'one'
,'two' => 'two'
)

as you suggested but it still did not work.

to eliminate the last piece of code that stayed the same, the one retrieving IDs and titles of posts belonging to custom taxonomy, i used get_posts() instead WP_Query. at the end array structure stayed the same. only after completely removing WP_Query and wp_reset_postdata() from metabox and from plugin, saving meta started to work.

i hope this is valuable info to you.

thanks a lot for all your help and hard work on piklist support.

Page 1 means i.e. I am editing “about us” page, and page 2 means I am editing “contact” page.

I was waiting for update to finish but it just stucks there. And the message to update does not go away.

it did not work with an array as you suggested. tried it already

tabify tabs do not reload the page