CC Mode 5.28 (C++); M-; and TAB disagree on comment indentation

[Eric Hanchrow <offby1@blarg.net>]

I'm not sure this is a bug, but it's surprising behavior.

With the following four-line program in a C++ buffer, with point
before the `y'

====================
ya ()
{
  // yow
}
====================

If I hit M-; the comment scoots over so that the `y' is at column 35.
If I then hit TAB, it scoots back so that the `y' is at column 5
(which is where it is above).  Perhaps there's a good reason for this,
but it took me by surprise.  I guess I'd expect M-; to leave the
comment where it is.

In fact, the node "Comment Commands" in the Emacs manual says 

        In C code, a comment preceded on its line by nothing but
        whitespace is indented like a line of code.

To me, that means that M-; should indeed leave the comment alone,
instead of scooting it over to column 35.

Emacs  : GNU Emacs 21.2.1 (i386-debian-linux-gnu, X toolkit, Xaw3d scroll bars)
 of 2002-03-22 on raven, modified by Debian
Package: CC Mode 5.28 (C++)
Buffer Style: gnu

c-emacs-features: (1-bit)

current state:
==============
(setq
 c-basic-offset 2
 c-comment-only-line-offset '(0 . 0)
 c-block-comment-prefix ""
 c-comment-prefix-regexp '((pike-mode . "//+!?\\|\\**") (other . "//+\\|\\**"))
 c-cleanup-list '(scope-operator)
 c-hanging-braces-alist '((brace-list-open) (brace-entry-open)
                          (substatement-open after)
                          (block-close . c-snug-do-while)
                          (extern-lang-open after)
                          (inexpr-class-open after) (inexpr-class-close before))
 c-hanging-colons-alist nil
 c-hanging-semi&comma-criteria '(c-semi&comma-inside-parenlist)
 c-backslash-column 48
 c-label-minimum-indentation 1
 c-offsets-alist '((string . c-lineup-dont-change)
                   (c . c-lineup-C-comments)
                   (defun-open . 0)
                   (defun-close . 0)
                   (defun-block-intro . +)
                   (class-open . 0)
                   (class-close . 0)
                   (inline-close . 0)
                   (func-decl-cont . +)
                   (knr-argdecl . 0)
                   (topmost-intro . 0)
                   (topmost-intro-cont . 0)
                   (member-init-intro . +)
                   (member-init-cont . c-lineup-multi-inher)
                   (inher-intro . +)
                   (inher-cont . c-lineup-multi-inher)
                   (block-open . 0)
                   (block-close . 0)
                   (brace-list-close . 0)
                   (brace-list-intro . +)
                   (brace-list-entry . 0)
                   (brace-entry-open . 0)
                   (statement . 0)
                   (statement-case-intro . +)
                   (substatement . +)
                   (case-label . 0)
                   (access-label . -)
                   (do-while-closure . 0)
                   (else-clause . 0)
                   (catch-clause . 0)
                   (comment-intro . c-lineup-comment)
                   (arglist-cont . 0)
                   (arglist-cont-nonempty . c-lineup-arglist)
                   (stream-op . c-lineup-streamop)
                   (inclass . +)
                   (cpp-macro . [0])
                   (cpp-macro-cont . c-lineup-dont-change)
                   (friend . 0)
                   (objc-method-intro . [0])
                   (objc-method-args-cont . c-lineup-ObjC-method-args)
                   (objc-method-call-cont . c-lineup-ObjC-method-call)
                   (extern-lang-open . 0)
                   (extern-lang-close . 0)
                   (inextern-lang . +)
                   (namespace-open . 0)
                   (namespace-close . 0)
                   (innamespace . +)
                   (template-args-cont c-lineup-template-args +)
                   (inlambda . c-lineup-inexpr-block)
                   (lambda-intro-cont . +)
                   (inexpr-statement . 0)
                   (inexpr-class . +)
                   (statement-block-intro . +)
                   (knr-argdecl-intro . 5)
                   (substatement-open . +)
                   (label . 0)
                   (statement-case-open . +)
                   (statement-cont . +)
                   (arglist-intro
                    . c-lineup-arglist-intro-after-paren)
                   (arglist-close . c-lineup-arglist)
                   (inline-open . 0)
                   (brace-list-open . +)
                   )
 c-delete-function 'delete-char
 c-electric-pound-behavior '(alignleft)
 c-indent-comments-syntactically-p nil
 c-tab-always-indent t
 defun-prompt-regexp nil
 tab-width 8
 comment-column 32
 parse-sexp-ignore-comments t
 auto-fill-function 'c-do-auto-fill
 comment-multi-line t
 comment-start-skip "/\\*+ *\\|//+ *"
 fill-prefix nil
 paragraph-start "[ 	]*\\(//+\\|\\**\\)[ 	]*$\\|^\f"
 adaptive-fill-mode t
 adaptive-fill-regexp "[ 	]*\\(//+\\|\\**\\)[ 	]*\\([ 	]*\\([-|#;>*]+[ 	]*\\|(?[0-9]+[.)][ 	]*\\)*\\)"
 )