Wordpress not detecting 404

I had to turn off permalinks in Wordpress cause missing pages were not detected. So right now I'm stuck with "ugly" URLs until this issue has been resolved.
I've started this thread in the WP support forums to try to get some help on this. So far nothing useful has turned up though.

Edit: I'll keep the broken permalinks because it's already indexed by some search engines. I'll try to install Wordpress from their SVN instead when i get some more time.