Game crashes when I disconnect from a server.

[=TFU= M-Coke]

Whenever I disconnect from a server it goes back to the menu for a spilt second but there is weird multi coloured patterns over the screen, then it crashes back to the desktop. And I'm pretty sure it ain't my graphics card (ATI 4850) works fine the rest of the time apart from the occasional crash when joining some servers like Kashan, and when the map changes but that is a straight crash to desktop that other people have reported.