Version: (using KDE KDE 3.5.5) Example: I set action to move message into folder but I forget to set which folder I have in mind. I can click "ok" and not even know there is something wrong, because KMail didn't warn me about missing part.
It is fixed now, although not as I would wish for. See: https://bugs.kde.org/show_bug.cgi?id=196352