Bug in Python re.sub() with re.MULTILINE?

>> import sys, os
>>> print sys.version
2.7.3 (default, Aug  1 2012, 05:14:39)
[GCC 4.6.3]
>>> print [os.uname()[i] for i in [0, 2, 3, 4]]
['Linux', '3.2.0-25-generic', '#40-Ubuntu SMP Wed May 23 20:30:51 UTC 2012', 'x86_64']
>>> import re
>>> pattern = r'int (\w+) = (.*?);'
>>> replace = r'\t\1 = \2,'
>>> text = 'int x = 5;\nint x = 5;\nint x = 5;\nint x = 5;\nint y = 5;\nint x = 5;\nint x = 5;\nint x = 5;\nint x = 5;\nint x = 5;\nint x = 5;\nint x = 5;\nint x = 5;\nint x = 5;\nint x = 5;\nint x = 5;\nint x = 5;'
>>> print text, "\n\n"
int x = 5;
int x = 5;
int x = 5;
int x = 5;
int y = 5;
int x = 5;
int x = 5;
int x = 5;
int x = 5;
int x = 5;
int x = 5;
int x = 5;
int x = 5;
int x = 5;
int x = 5;
int x = 5;
int x = 5;


>>> print re.sub(pattern, replace, text, re.MULTILINE), "\n\n"
    x = 5,
    x = 5,
    x = 5,
    x = 5,
    y = 5,
    x = 5,
    x = 5,
    x = 5,
int x = 5;
int x = 5;
int x = 5;
int x = 5;
int x = 5;
int x = 5;
int x = 5;
int x = 5;
int x = 5;


>>> print re.sub(pattern, replace, text), "\n\n"
    x = 5,
    x = 5,
    x = 5,
    x = 5,
    y = 5,
    x = 5,
    x = 5,
    x = 5,
    x = 5,
    x = 5,
    x = 5,
    x = 5,
    x = 5,
    x = 5,
    x = 5,
    x = 5,
    x = 5,


>>> print re.subn(pattern, replace, text, 0, re.MULTILINE)[0], "\n\n"
    x = 5,
    x = 5,
    x = 5,
    x = 5,
    y = 5,
    x = 5,
    x = 5,
    x = 5,
    x = 5,
    x = 5,
    x = 5,
    x = 5,
    x = 5,
    x = 5,
    x = 5,
    x = 5,
    x = 5,


>>> regex = re.compile(pattern, re.MULTILINE)
>>> print regex.sub(replace, text)
    x = 5,
    x = 5,
    x = 5,
    x = 5,
    y = 5,
    x = 5,
    x = 5,
    x = 5,
    x = 5,
    x = 5,
    x = 5,
    x = 5,
    x = 5,
    x = 5,
    x = 5,
    x = 5,
    x = 5,