forward-comment, C-M-a and C-M-e problems in bibtex-mode

[Dan Nicolaescu]

If I have a bib file containing:

@Comment blah blah blah
@Comment blah blah blah

Doing:
M-: (goto-char 1) RET M-: (forward-comment 2) RET M-: (point) RET

prints: 
1

`forward-comment' should move the cursor if a comment follows the point. 

If @ is replaced with % (the other comment character), then
forward-comment works as expected. 

Pressing C-M-a when inside a bibtex entry moves the cursor to the
beginning of the entry, but pressing it again does not move to the
previous entry. The same is true for C-M-e.
All modes support this type of navigation using C-M-{a,e}