When does it throw you to the desktop?
What I've experienced may or may not be related to the problem you're having. But here's a brief explaination.
I've had a long-running problem (that actually started before 1.4). Occassionally, after entering the AH program and hitting any tab (or even any area on the clipboard to select H2H, online, etc.), I get dumped to desktop. The only thing that I've found to correct it is to uninstall, delete the HTC folder and reinstall.
Serious pain in the butt!
I wish I could figure out why this is occuring. I usually see it after a rare loss of connection in the main arena, but everytime I loose host connection in H2H. The smart thing for me in H2H is to quit before the host closes the game.
Reinstall is the only thing that fixes the problem for me.
If this is anything like your problem Habicht, I sure like to hear some fix suggestions too!