> From: Mark Kennedy <mark.t.kennedy@gmail.com>
> Date: Sat, 13 Nov 2021 09:52:21 -0500
> Cc: 51794@debbugs.gnu.org
>
> i'm willing to attempt to debug it myself but not via the -Q route.  i
> prefer to focus on where the bad input event stream is being created.
> any suggestions about where to put an elisp or C breakpoint to go
> after this?

In keyboard.c, under "case MOUSE_CLICK_EVENT:", step through the
code until you get to this line:

            position = make_lispy_position (f, event->x, event->y,
                                            event->timestamp);

then step into make_lispy_position, and see what it produces.

(I hope I got the code right; apologies if not.)