Richard Stallman <rms@gnu.org> writes:

> From: Toby Allsopp <Toby.Allsopp@navman.com>
> Subject: auto-fill in c-mode messes up incomplete comments
> To: emacs-pretest-bug@gnu.org
> Cc: emacs-snapshot@packages.debian.org
> Date: Tue, 28 Nov 2006 11:48:39 +1300
>
>>From a shell prompt:
>
> emacs -q /tmp/tmp.c
> M-x auto-fill-mode
> /*
> * 
>
> (That's / * <return> * SPC).
>
> When typing the final space, the second line gets deleted.  Pressing
> return instead messes it up differently.  This seems to be a problem
> with c-mask-paragraph.

Toby, does the following fix your problem?