I have two blogs, one running WP 3.3 and another running 3.3.1.
On both blogs I have a page using JWplayer to play a YouTube playlist.
Using v1.5.4, both pages work fine.
When upgrading to v1.5.8, the player does not appear on the page, and gives no error messages.
When reverting to v1.5.4, both pages again work fine.
The page contains only the JWPlayer shortcode:
[jwplayer config="Video player" playlistfile=http://gdata.youtube.com/feeds/api/playlists/36B78CA52746B8ED]
You can see the v3.3/v1.5.4 page that works correctly here:
and the v3.3.1/v1.5.8 page that doesn't work here: