Semi frozen User interface

[elegance]

When running 2 accounts at the same time, after few sorties one of them gets semi frozen user interface (map+aar+brigade list). Interface is really laggy, white squares on map (or complete whiteout), no reaction to mouse clicks for few seconds. However once I spawn in everything is fine. Restarting the affected account does get rid of it, however the next time I get this much sooner (after 1-2 sorties). Overlay fps counter (ati tray tools) is showing steady 2 fps when at the user interface. Mac users seem to be suffering from this as well. Anybody else getting this?

Athlon x2 4200@2.7GHz

Radeon 4830@stock 512MB

X-fi xtreme gamer

4GB Ram

On a side note: still getting font and graphics corruption when alt-tabbing between accounts (mainly when loading, occasionaly when spawned in)