I’ve noticed this a couple of times and wondered if it can be replicated by anyone.
If you are using the media uploader, the first time (and every time after that if you don’t make a change) the file output is a string, for instance:
'company_logo' => string '1701' (length=4)

But if you remove the image and attach another (or the same one) then it changes to an array:

'company_logo' => 
    array (size=1)
      0 => string '1701' (length=4)

Means you have to write a case for an array or not, as well the additional steps to extract the image details.

Example of the field setup:

piklist('field', [
	'type' => 'file',
	'field' => 'company_logo',
	'label' => 'Logo',
	'options' => [
		'title' => 'Add Logo',
		'button' => 'Add Logo',
		'modal_title' => 'Add Logo'
	]
]);

I’m running the latest version of the plugin v0.9.3.6.