cmd_scrollTop fails to update window.scrollY, therefore scroll_horiz_complete would result in undoing it.
reordering the functions in scroll-top-left fixes it.

interactive("scroll-top-left",
    "Scroll the current frame all the way to the top left",
     function (I) { scroll_horiz_complete(I.buffer, -1);
                    I.buffer.do_command("cmd_scrollTop"); });