#4 - Nov. 16, 2010, 8:20 a.m.
This sounds suspiciously like something in your UI is interfering or you have corrupted files.
I'd first strongly recommend a full reset UI and see if this happens prior to readding any addons in.
If that doesn't seem to help, running repair tool would be the next best step.
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