> I applied the patch and rebuilt Emacs, then started with my
 > initializations under gdb.  Emacs came up fine, then I type C-h C-a and
 > it aborted in unshow_buffer; the backtrace is almost identical to the
 > one I posted previously.

Why am I not surprised?  Though, it doesn't abort here.

 > Then I started Emacs again, started Gnus, as
 > with your first suggested patch with set_marker_both (w->buffer, BEG,
 > BEGV)

I suppose you mean set_marker_both (w->pointm, w->buffer, BEG, BEGV)
here.

 > the display was unstable (unselected window at first blank, then
 > blank fringe), then tried `h' and it worked a few times but the response
 > was slow, and then (after `h' not C-g) Emacs aborted in unshow_buffer;
 > backtrace below.  Just out of curiosity (since I don't understand the
 > code), I rebuilt again with the following call (old_buffer instead of
 > w->buffer):
 >
 >        set_marker_both
 >  	(w->pointm, old_buffer, BUF_PT (current_buffer), BUF_PT_BYTE (current_buffer));
 >
 > This did not cause an abort with C-h C-a nor with h in Gnus, but it
 > showed the same problem of point in the non-selected window jumping to
 > point-min, despite not passing BEG and BEGV.

The strange thing about this is that when old_buffer is not the current
buffer, this will set the marker in the wrong buffer which should cause
an abort.  But as I stated earlier I'm still completely lost here :-(

Anyway, I attached another patch.  Things are getting more and more
complicated because I have zero experience working with markers in C.

martin