Potential regex bug in python -- why isn't "o'clock" part of the match for re.findall()?

regex.py

#! /usr/bin/env python
# -*- coding: utf-8 -*-

# License: CC-BY-NC-SA 3.0

import re
import codecs

# download kate_chopin_the_awakening_and_other_short_stories.txt
# from Project Gutenberg:
# http://www.gutenberg.org/ebooks/160.txt.utf-8
# with wget:
# wget http://www.gutenberg.org/ebooks/160.txt.utf-8 -O kate_chopin_the_awakening_and_other_short_stories.txt


# match for something o'clock, with valid numerical time or
# any English word with proper capitalization

oclock = re.compile(r"""
                    (
                          [A-Z]?[a-z]+ # word mit max. 1 capital letter
                        | 1[012]       # 10,11,12
                        | [1-9]        # 1,2,3,5,6,7,8,9
                    )
                    \s
                    o'clock""",
                    re.VERBOSE)

path = "kate_chopin_the_awakening_and_other_short_stories.txt"

print
print "re.search()"
print
print u"{:>6} {:>6} {:>6}\t{}".format("Line","Start","End","Match")
print u"{:=>6} {:=>6} {:=>6}\t{}".format('','','','=====')

with  codecs.open(path,mode='r',encoding='utf-8') as f:
    for lineno, line in enumerate(f):
        atime = oclock.search(line)
        if  atime:
            print u"{:>6} {:>6} {:>6}\t{}".format(lineno,
                                            atime.start(),
                                            atime.end(),
                                            atime.group())


print
print "re.findall()"
print
print u"{:>6} {:>6} {:>6}\t{}".format("Line","Start","End","Match")
print u"{:=>6} {:=>6} {:=>6}\t{}".format('','','','=====')
with  codecs.open(path,mode='r',encoding='utf-8') as f:
    for lineno, line in enumerate(f):
        times = oclock.findall(line)
        if times:
            print u"{:>6} {:>6} {:>6}\t{}".format(lineno,
                                            '',
                                            '',
                                            ' '.join(times))


print
print "re.finditer()"
print
print u"{:>6} {:>6} {:>6}\t{}".format("Line","Start","End","Match")
print u"{:=>6} {:=>6} {:=>6}\t{}".format('','','','=====')
with  codecs.open(path,mode='r',encoding='utf-8') as f:
    for lineno, line in enumerate(f):
        times = oclock.finditer(line)
        for m in times:
            print u"{:>6} {:>6} {:>6}\t{}".format(lineno,
                                            m.start(),
                                            m.end(),
                                            m.group())

Check out the explanation on StackOverflow.