Source file mode line not update when committing with VC

[Stephen Berman]

I have a local development branch of the Emacs trunk and since at least
yesterday, when I commit changes by typing `C-c C-c' in the *vc-log*
buffer, the mode line of the source files is no longer automatically
updated to show the latest Bzr revision number.  I can't be sure this
didn't start happening earlier -- the last commit I made before
yesterday was on April 27 and I don't remember if the mode line failed
to update then.  Has anyone else noticed this?  If not, does anyone have
an idea what could have caused this change?  Is there some variable
controlling this that I may have accidentally changed?

Steve Berman