[Note. All of these also occur in real XEmacs usages. Maybe problems like these also cause the crashes Colin sees using electric-buffer-list, because that uses the window configuration stuff] Because in the window configurations, window sizes are stored in pixels, but frame-sizes in lines we get breakage when there is a redisplay in the save-window-excursion with a new fontheight. xemacs -vanilla -eval '(progn (set-face-font (quote default) "-*-courier-medium-r-*-*-*-140-*-*-*-*-iso8859-*") (save-window-excursion (redisplay-device)))' xemacs -vanilla -eval '(progn (set-face-font (quote default) "-*-courier-medium-r-*-*-*-60-*-*-*-*-iso8859-*") (save-window-excursion (redisplay-device)))' [You can actually scroll the cursor off screen with this last one!]. There is code that tries to deal with this (and other frame size changes) in Fset_window_configuration but it fails in the font size change case (because in XEmacs 21.0 font size changes preserve the lines*colums size, not the pixel size). One identified it is easy to come up with other such problems xemacs -vanilla -eval '(save-window-excursion (set-specifier default-toolbar nil) (redisplay-frame))' One could probably continue to do this ad infinitum, (and I have actually seen this happen before). Solution? Maybe we should not blindly copy the window sizes in pixels... Instead we should try to preserve relative sizes. i.e. new-window-width = total-available-width * (old-window-width / old-total-avaliable-with) and the same for height. Of course the real code should do this without floats, deal with over/underflows and should allocate the rounding error pixels to one of the windows. One could also argue that save-window-configuration should also save the relevant specifiers for the tool-bar and the scrollbar etc. Jan