When I create a new node / edit a node to attach a youtube video via media file selector, then I search video by typing Video ID, it will display errors about "Warning: Illegal string offset 'link' in media_youtube_add()".

It should be caused when only one result found in search.
As displayed in attached screenshot, it is no wrapper for $search['entry'] thus error occurred.

Screen Shot 2013-05-07 at 18.37.00.png109.66 KBenomoto