Subject: bug#16377: Undo Tree regression: (error "Unrecognized entry in undo list undo-tree-canary")

From: Stefan Monnier <[email-masked]>
Date: Wed, 22 Jan 2014 13:56:12 -0500

> Are there circumstances in which `primitive-undo' doesn't add to
> `buffer-undo-list'?

Of course: if there are no changes until the next undo boundary, then
primitive-undo just doesn't do anything other than pop that
undo boundary.
And primitive-undo doesn't add any boundary, so it can end up with no
change at all to buffer-undo-list.

        Stefan