Re: xasserts and vertical motion.

[Richard Stallman]

    b) they don't check for _structural_ incoherence (namely that Emacs'
    internal data structures are not garbled), but for _visual_
    incoherence.  But for debugging this one needs information about what
    kind of things happen on the screen at the time, and just in what
    manner some expectations might get violated.  This is much easier to
    get when Emacs remains operative and gets a chance to _display_ the
    result of the operation instead of committing suicide.

You should be able to continue by typing the GDB `return' command
and then `c'.  Does it work?