smhmic

Your code uses the global $ variable — which is not a good practice. It worked only because your theme replaces the jQuery file loaded by WordPress with jQuery from Google CDN — also poor practice. It’s poor practice because WordPress loads jQuery in “noConflict” mode (which does not associate the $ variable with jQuery), and some plugins rely on noConflict mode.

The Responsive Menu plugin breaks your code because it re-activates jQuery’s noConflict mode.

Your fix: replace $ with jQuery in this code:

$(function(){
  $('#testimonial-container-demo').mixItUp();
});

You’re right, mrfoxtalbot, your code is doing something wrong — it wouldn’t even work on stock WordPress. $ is not a function because WordPress loads jQuery in “noConflict” mode.

Solution: Change each of the “$”s to “jQuery” (note the case).

I noticed something in the old-style media upload screen. (Using WP v3.9.1, but some plugins still employ the old-style media uploader.)

With a comma separator, filtering works, but the count for grouped mime types at the top is always zero, and PHP notices are thrown from wp-admin/includes/media.php on line 2316.

With a pipe separator, no notices are thrown, but no media items appear in the list (yet — strangely enough — the count is correct).

I was able to get the correct count and avoid the notices by using a pipe separator on the old media upload form…

// WordPress v3.9.1 function get_views() and old-style upload form expect
// pipe separators, whereas media upload dropdown filter expects commas.
$glue = in_array( $pagenow, array( 'upload.php', 'media-upload.php' ) ) ? '|' : ',';

… and get the media items to appear by adding this filter:

global $pagenow;
if( 'media-upload.php' == $pagenow )
	add_filter( 'pre_get_posts', 'old_media_upload_form_fix', 99 );
function old_media_upload_form_fix( $wp_query ) {
	if ( $query_var = $wp_query->get( 'post_mime_type' ) )
		$wp_query->set( 'post_mime_type', str_replace( '|', ',', $query_var ) );
	return $wp_query;
}

Note you can handle the comma vs pipe difference directly within the function, by choosing the character based on context. See my implementation below (implemented as a standalone filter):

add_filter( 'post_mime_types', 'group_post_mime_types', 99 );
function group_post_mime_types( $post_mime_types ) {

	// WordPress function get_views() expects pipe separators,
	// whereas media upload dropdown filter expects commas.
	global $pagenow;
	$glue = 'upload.php' == $pagenow ? '|' : ',';     

	$mime_types_grouped_by_name = array();
	foreach( $post_mime_types as $mime => &$labels ){
		$mime_types_grouped_by_name[ $labels[0] ][ $mime ] = $labels;
	}
	$new_post_mime_types = array();
	foreach ( $mime_types_grouped_by_name as $name => &$mime_labels ) {
		$new_post_mime_types[ implode( $glue, array_keys( $mime_labels )) ] = reset( $mime_labels );
	}
	return $new_post_mime_types;
}

I’ve tested and this works well in v3.9.1.

jQuery Cycle — the code that powers this plugin — is not responsive. There are some workarounds, all of which require a small bit of coding.

But if you are comfortable coding, then I recommend using a solution that doesn’t need to be hacked into behaving semi-responsively. I like this one: https://www.woothemes.com/flexslider/