We are seeing a *very* strange problem. We have a number of identical computers with identical KDE setups from Debian stable.

On one of them, every once in a while kmail stops responding to user input. It has *not* crashed. For example it responds to dbus messages, and the automatic mail check still works (and the user interface is redrawn). However any user input (keyboard, mouse both movement and clicking) is simply not processed, as if it was never sent to the window in question. Other kde and non-kde applications (for example emacs) on that system work fine.

Clicking the "close window" button in the title brings up the "this application is not responding, would you like to kill it" message.

I have never seen anything like it and am at a loss of what to do and how to start debugging this problem. We have tried to identify differences in the setup/usage for that user and came up with two things:
   a) they use focus-follows-mouse
   b) they sometimes login from another computer

W.r.t. (a) we have disabled focus-follows-mouse and the problem still persists.

On (b), they sometimes log in from a different computer and have ignored the message "there is already a running instance of kmail". I thought we eliminate this by making sure no kmail or related kio processess are running and then starting kmail again. Again, the problem still persists.

We have recently tried deleting all config in .kde relating to kmail, but the problem still persists.

Do you have any idea what is going on?

Thanks,
   Florian

Reproducible: Always