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Python returns a different exit status when an exception is raised and -m is used as opposed to just running a module.
A short example, let's call it foo.py:
 def main():
 raise ValueError()
 if __name__ == '__main__':
 main()
When run with python foo.py the exit status of the process is 1. If run with python -mfoo the exit status of the process is 255.

Technically, it returns -1 (which later gets coerced to an unsigned value).
However, there's no good reason for the inconsistency - the offending line (663) in main.c should be changed to be:
 sts = (RunModule(module, 1) != 0);
It is currently just:
 sts = RunModule(module, 1);
An additional test in test_cmd_line_script is also needed to ensure that both variants give a returncode of 1 in the future.

Fixed for 3.3. Does this need to be back ported as well?

And by 'Fixed' I of course meant 'Patched, awaiting review'.

New changeset fcbd3bda7c0f by Senthil Kumaran in branch '3.2':
Fix issue # 15033 - Return the proper exitcode for failure when modules are invoked using -m switch. Patch contributed by Jeff Knupp
http://hg.python.org/cpython/rev/fcbd3bda7c0f
New changeset 1186d68715cc by Senthil Kumaran in branch 'default':
Fix issue # 15033 - Return the proper exitcode for failure when modules are invoked using -m switch. Patch contributed by Jeff Knupp
http://hg.python.org/cpython/rev/1186d68715cc 

New changeset 55b3de6d701e by Senthil Kumaran in branch '2.7':
Fix closes issue # 15033 - Return the proper exitcode for failure when modules are invoked using -m switch. Patch contributed by Jeff Knupp
http://hg.python.org/cpython/rev/55b3de6d701e 

Thanks for the patch Jeff and thanks for the guidance, Nick. 
Committed this in all branches.