Well, first things first, does it still do that after disabling your addons?
(and I mean all of them, sometimes completely unrelated things can cause bugs)
I've found this question to mostly be pointless. People say "yes, I've disabled them all and it still does it" even though they haven't.
OP - post a screenshot with all addons disabled, and then we might be able to help more.
EDIT: Also, as to it only happening in dungeons and cities, try turning off any faders enabled on your minimap addons. Although, with all addons disabled, this'll go a long way to proving if there's an issue with the addon or the game files.
NOTE: If the problem still exists with all addons disabled, run repair.exe.
1. Exit WoW, rename "Interface" and "WTF" to something else, like add "_bk" or what ever on the end.
2. Start the game and login, is the problem still there?
3. To restore, delete new "Interface" and "WTF" folders then rename your "_bk" tagged once back to their original names, restoring all addon settings.
Beats having to figure out what addons to turn on later, hehe. Also uses completely default configurations and it may help fix some issues, CVars change over time you see -especially if you use a ooold .wtf config file.
He posted a screenshot to elaborate.. look at it? You may have a proxy blocking the site, so here is the URL:
Code:http://img543.imageshack.us/img543/6637/wowscrnshot112810211951.jpg
There's a common proxy program (adblock?) that blocks imageshack.us, so you would not have seen the thumbnail. Although, that would simply indicate you're using IE and not FireFox with NoScript, in which case I ask.. WHHHY?
Trying with all addons disabled would certainly be a good start, and guessing in this case that the addon you are using for your minimap is Sexymap so that should be the first one you try taking out.
Odd behaviour is one thing, but that is something beyond the usual odd behaviour.
Try clearing the contents of the cache folder when wow is not running, should the disabling of addons not work, and as a last resort try the repair feature.
I used to get that (on minimap and in the world) when my video card was overheating
May be a driver issue, Cata did change some of the engine so make sure you update your drivers (do a system restore backup first, just in case).