Apps crash when quitting...

I have this recurrent behaviour with Panther that drives me mad. For not apparent reason, every single app will crash when I quit them. All the standard tricks to troubleshoot this (repair permissions, fix prebinding, flush system/app font cache, etc.) have failed to fix the problem. The only way to fix this is to re-install the latest combo update (in this case, 10.3.9). And even then, the problem will only go away for a few days. It always comes back.

FYI, I run a plain vanilla system, no APE/haxies or similar.

What the **** is going on? Thanks!