Ok. After investing some more, and still not obviously seeing what's wrong, I find that: * sometimes, after running xmonad for a long time, I can't kill xclock (for example), or any other app that uses the wmdelete protocol (requiring us to send delete notification). * quitting out completely, and logging back in, with a new build, and everything works. * restarting, and it still works. Also, the case when we need to send this event is still spotted correctly,so the bug is in the X11-extras code I suspect. I'll look into this some more if I can work out how to reproduce it. David, can you pull all the latest patches, rebuild and install xmonad. Quit X, log back in, then check if you can kill xclock? -- Don