I checked for the existence of this bug in 2 other python versions today.  It's present in CPython 3.4.1, but CPython 2.7.5 doesn't exhibit the issue.


Python 2.7.5 (default, May 15 2013, 22:43:36) [MSC v.1500 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import os.path
>>> os.path.isabs(r"\\server")
True
>>> os.path.isabs(r"\\server\share")
True
>>> os.path.isabs(r"\\server\share\folder")
True
>>> os.path.isabs(r"\\server\share\folder\folder")
True
>>>


Python 3.4.1 (v3.4.1:c0e311e010fc, May 18 2014, 10:38:22) [MSC v.1600 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import os.path
>>> os.path.isabs(r"\\server")
True
>>> os.path.isabs(r"\\server\share")
False
>>> os.path.isabs(r"\\server\share\folder")
True
>>> os.path.isabs(r"\\server\share\folder\folder")
True
>>>