Don't know yet if the code change belongs in Undo Tree or Emacs but
the recipe is:
• Start Emacs in scratch buffer with global-undo-tree-mode enabled
• Go to BOB and insert "xxx"
• Select first line
• undo-tree-undo in region
• undo-tree-redo in region
• Navigate down (redo)*
• Navigate up (undo)
Upon the navigate up, this error occurs:
Debugger entered--Lisp error: (error "Unrecognized entry in undo list undo-tree-canary")
signal(error ("Unrecognized entry in undo list undo-tree-canary"))
error("Unrecognized entry in undo list %S" undo-tree-canary)
call-interactively(undo-tree-visualize-undo nil nil)
* Sometimes the navigate down hangs with backtrace:
Debugger entered--Lisp error: (quit)
call-interactively(undo-tree-visualize-redo nil nil)
Don't know if it's related or not.
This recipe does not cause a problem with Emacs 24.3.
The following commit is suspicious:
Author: Aaron S. Hawley <address@hidden
Date: Tue Jan 8 14:13:31 2013 -0500
* lisp/simple.el (primitive-undo): Move from undo.c.
* src/undo.c (Fprimitive_undo): Move to simple.el.
(syms_of_undo): Remove declaration for Sprimitive_undo.
* test/automated/undo-tests.el: New file.
The commit moved primitive-undo from C to Elisp. In the process, it
added an else condition not present in the C code:
+ (t (error "Unrecognized entry in undo list %S" next)))))
The consequence of this bug is that when using Undo Tree, recent undo
history can become completely inaccessible.
I should note that if I don't undo in region, Undo Tree has never run
into any problems with the Emacs on trunk.