bug#4773: 23.1.50; VC: vc-next-action fails to add file to CVS if used from a file buffer

In GNU Emacs 23.1.50.1 (i686-pc-linux-gnu, GTK+ Version 2.8.20)
 of 2009-10-20 on leeloo
Windowing system distributor `RealVNC Ltd', version 11.0.3370
configured using `configure  '--with-x''


Typing C-x v v in a file buffer for a file in a CVS-controlled directory
currently complains that the file is not in a version controlled
directory and prompts me to choose a backend (and this prompt does not
accept CVS as an option).
Using vc-dir, 'v' can be used on the unregistered file without issues,
so it's not a blocking problem, but it is annoying.
Once the file is registered, further VC actions from inside the buffer
work just fine.