Version:           1.5.2 (using KDE KDE 3.1.2)
Installed from:    Debian testing/unstable Packages
Compiler:          -irrelevant- -irrelevant-
OS:          Linux

While filters are active in the background, the GUI appears to
be freezed. Normally this is not a problem because the filtering 
doesn't take long. But if you pipe a mail through some other 
program, like Spam Assassin, the process can make the GUI
temporarily useless.

I would, though, be able to access some of my mail folders in the
meantime. This is probably a thread issue, and threads seem to
be generally unattractive to the KDE-team... ;-)

Anyway, this just a suggestion.