Any way to make vc-toggle-read-only work again?

[Ilya Zakharevich]

On v23.1.1, vc-toggle-read-only is disabled (mentioning some
irrelevant reason).  Is there any way to make VC subsystem work again?

 [ AFAIU, the recommended way — to use vc-next-action — is completely
   broken.  In my experiments, it silently (!) removes the edits I
   make to the file (no question asked, and only a very unhelpful
   message about what happens [*]).  No undo is possible! ]

     [*] I expect it to do "save", while it does "restore".
         Unfortunately, the language it uses for "save"/"restore" is
         "check in"/"check out", which do not differ sufficiently
         (which one means which?) to make the "status message" easily
         comprehensible.

Thanks,
Ilya