#1 - Dec. 14, 2009, 8:32 p.m.
Have you tried resetting your UI? It sounds like something has corrupted or there is a conflict.
There is a known issue on this at the moment, but I'd definitely give reset UI a try as well.
To do a full reset UI, you will want to save your addons in another spot if you wish to preserve them.
Then rename/delete or move your WTF, Cache and Interface folders while WoW is shutdown. Reboot your system.
Note, if you are running Vista make sure your permissions are set so it does not undo your changes.
More detailed instructions for different operating systems, including Macs are here.
http://us.blizzard.com/support/article.xml?articleId=18761&searchQuery=reset%20UI&pageNumber=1