Emacs on Linux crashes in XQueryPointer

[Alan Shutko <ats at acm dot org>]

I've got a Debian Sid box running XFree86 (debian package 4.3.0-7).
If I pipe emacs -q from it (emacs 21.3 or CVS, doesn't matter) to my
WinXP box running XWin 6.7.0.0-1, click the window to get rid of the
Emacs intro screen, and select text right to left, Emacs crashes with 

X protocol error: BadWindow (invalid Window parameter) on protocol request 38

Backtrace shows that this is occuring in XQueryPointer, called from
various points in Emacs.  I can reproduce this every time.  Running
Emacs in synchronous mode shows the same results.  This does not
happen running Emacs to the local Linux X server.  This also does not
show up with the Cygwin packaged Emacs 21.2.

Any ideas on what's causing this, or how I could help narrow it down
some more?  This makes Emacs extremely unstable displaying on
Cygwin/X for me, since I have to try to avoid using the mouse at all,
or else I might crash Emacs.

-- 
Alan Shutko <ats@acm.org> - I am the rocks.
My computer's getting jealous.... of the time I spend with my wife.