With the diffs Allen gave to me, I've built a new Xserver which works
fine with SE/30.  The cause of the problem appears to be grfmmap()
routine failing to map SE/30's frame buffer correctly.  I changed
mmap() back to ioctl() and the problem went away.  I'm not sure as to
why mmap() doesn't work with SE/30's internal video, but I've been
investigating.  It looks like mmap() maps the declaration ROM instead
of the frame buffer into process' virtual address space.

Anyway, the working server binary is placed at:

ftp://puma.bevd.blacksburg.va.us/private/kenn/Xmacbsd-960127.tar.gz

Untar it in /usr/X11R6/bin directory.  Don't forget to mv your old
server to, for instance, Xmacbsd.old before untarring the new one,
just in case it doesn't work for you.

Note: the server file may be moved to a different place later.

Have fun!

ken