The behavior of os.path.abspath differs between Mac OS X and Windows. It seems like a bug that, on Windows, abspath strips trailing whitespace:
Windows:
>>> from os.path import abspath
>>> abspath('start  ') + 'END'
'c:\Users\jgray\code\startEND'
                         ^
Mac:
>>> from os.path import abspath
>>> abspath('start  ') + 'END'
'/Users/jgray/code/start  END'
                        ^^

I have only tested with python 2.7.3 (Enthought distribution), 32-bit, and only Mac 10.8.2 and Windows 7.