Auto-wrap inside comments with numbered list is broken (regression)

What steps will reproduce the problem?

vim -N -u NONE
:setl tw=80 fo+=nc comments=:#
:call setline(1, '# 1 ' . repeat('x', 70))
:normal! A foobar

What is the expected output?

#1 xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
# foobar

What do you see instead?

#1 xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
    # foorba

What version of the product are you using? On what operating system?

This is the latest Vim on Ubuntu/x86. The problem does not occur with Vim 7.3.0 
on Windows/x86 or Vim 7.1.138 on Ubuntu/x86.

:version
VIM - Vi IMproved 7.3 (2010 Aug 15, compiled Jun 20 2012 16:55:09)
Included patches: 1-562
Big version with GTK2 GUI.  Features included (+) or not (-):

Please provide any additional information below.

I encountered this when editing a shell script header (ft=sh), and whittled it 
down to the steps above. There must be both a comment leader (#) and a number 
following it for the bug to occur, together with "n" and "c" in 'formatoptions'.

Original issue reported on code.google.com by sw...@ingo-karkat.de on 20 Jun 2012 at 3:41

proteanthread / vim

Auto-wrap inside comments with numbered list is broken (regression) #65