Keymaps on images have pretty much stopped working

[David Kastrup]

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Please describe exactly what actions triggered the bug
and the precise symptoms of the bug:

I use keymaps for mouse clicks on images to get clickable reactions.
At times the keymap for a different image gets called, more often the
right one, but most often just the usual mouse bindings get used.
This is pretty much random.  Except that big images tend to have a
better chance to be hit.  No wait: there is a difference involved
here: the big images (which don't work reliable either) are done with
the display property of an overlay, and the small images (which very
much never work) are implemented as a before-string property, with a
string that has a single-character content made clickable and visible
by display and other properties.

The mouse-over highlighting seems to work completely reliable, though.
C-h k followed by a click on either image bombs out with a backtrace:

Debugger entered--Lisp error: (wrong-type-argument number-or-marker-p (:file 
"/home/dak/tex/diss/diss.prv/tmp2444xFT/prev002.png" :type png :ascent 76 
:heuristic-mask t))
  string-key-binding([(mouse-2 (#<window 3 on kalmantheory.tex> 24 ... 10270702 
... 24 ... ...))])
  describe-key([(mouse-2 (#<window 3 on kalmantheory.tex> 24 ... 10270702 ... 
24 ... ...))] 1)
  call-interactively(describe-key)



In GNU Emacs 21.3.50.6 (i686-pc-linux-gnu, GTK+ Version 2.2.1)
 of 2004-01-03 on lola.goethe.zz
configured using `configure '--prefix=/usr/local/emacs-21' '--with-gtk''

Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: en_US
  locale-coding-system: iso-latin-1
  default-enable-multibyte-characters: t

Major mode: LaTeX

Minor modes in effect:
  reftex-mode: t
  auto-compression-mode: t
  desktop-save-mode: t
  display-time-mode: t
  iswitchb-mode: t
  mouse-wheel-mode: t
  menu-bar-mode: t
  unify-8859-on-encoding-mode: t
  line-number-mode: t

-- 
David Kastrup, Kriemhildstr. 15, 44793 Bochum