In win32 and linux platform, os modules has diffreent output order, is it a bug?

[Honghe Wu]

env: python 2.7.3

6 test files' name in a directory as below:
12ab  Abc  Eab  a1bc  acd  bc

the following is test code:
for root, dirs, files in os.walk(os.getcwd()):
    print files

the output in win32 platform is:
['12ab', 'a1bc', 'Abc', 'acd', 'bc', 'Eab']

but in linux is：
['Eab', 'acd', 'a1bc', '12ab', 'bc', 'Abc' ]

they are so different. a bug?