I have noticed an issue recently where adding YouTube clips into the Media browser works, but the thumbnail image pulled in from YouTube breaks. Ideally I'd like to be able to add my own thumbnails to this, but that aside, a working model would do! I haven't changed anything since it was installed, no permissions changes etc.
In this image you can see the 3 older media clips (at the bottom) with the thumbnails pulled in from YouTube and then the most recent three there (at the top) with broken images. Any ideas?