Does it help ?
http://pervalidus.port5.com/tmp/XWin.exe.stackdump
I got it with all latest packages while shutdowning the server
running my latest IceWM build (the first with working
fontconfig support (--enable-gradients --enable-antialiasing).
A month ago it'd just crash at startup with the above options
enabled, but the stackdump was from IceWM. It never crashed
without them.
waiting for X server to shut down ..........
xinit: X server slow to shut down, sending KILL signal.
waiting for server to die ...
xinit: Can't kill server
[1]+ Done startx
I couldn't reproduce it. Can the window manager cause it ?