Fix. Your. Game.

Q u o t e:
Why do you still get random DCs in battlegrounds and then sit at loading screen until you get deserter debuff? Its been weeks since 4.0, this crap us getting old. Disable the stupid debuff until you can get it together.

If you haven't already tried a full and proper reset of your interface, I'd recommend it - then test prior to loading back ANY addons.

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

While this may not be your issue, many have found this helpful for both disconnects and some cases of excessive lag in instances.