undo error

[Jesper Harder]

When I press undo (`C-_') twice in a buffer where undo information
has been disabled -- i.e. `buffer-undo-list' is t -- I get this
backtrace the second time:

Debugger entered--Lisp error: (wrong-type-argument listp t)
  car(t)
  (while (car tail) (when (integerp ...) (let ... ... ... ... ...)) (setq prev 
tail tail (cdr tail)))
  (let ((tail buffer-undo-list) (prev nil)) (while (car tail) (when ... ...) 
(setq prev tail tail ...)))
  (let ((modified ...) (recent-save ...)) (unless (eq last-command ...) (setq 
undo-in-region ...) (if undo-in-region ... ...) (undo-more 1)) (let (...) (or 
... ...) (when ... ... ...)) (undo-more (if ... ... 1)) (unless undo-in-region 
(puthash buffer-undo-list pending-undo-list undo-equiv-table)) (let (... ...) 
(while ... ... ...)) (and modified (not ...) 
(delete-auto-save-file-if-necessary recent-save)))
  undo(nil)
  call-interactively(undo)



In GNU Emacs 21.3.50.46 (i686-pc-linux-gnu, GTK+ Version 2.0.2)
 of 2004-02-09 on defun.localdomain
configured using `configure '--with-gtk''