My current list of changed_files() (command from the code)
% hg status --added --modified --no-status
Lib\idlelib\RstripExtension.py
Misc\ACKS
Misc\NEWS
Lib\idlelib\idle_test\mock_idle.py
Lib\idlelib\idle_test\test_rstrip.py

but
F:\Python\dev\py33>pcbuild\python_d tools/scripts/patchcheck.py
...
Misc/ACKS updated ... NO
Misc/NEWS updated ... NO

The problem is that 'Misc/ACKs' is not in the list, even though 'Misc\ACKS' is ;-(.

One possible fix is to conditionally change '\' to '/' in the file list, or maybe just in special_files, as that seems to be the only category affected.

Another is to change line 156 (3.3) from
    special_files = {'Misc/ACKS', 'Misc/NEWS'} & set(file_paths)
to
    special_files = {'Misc/ACKS', 'Misc/NEWS', 'Misc\ACKS', Misc\NEWS'} & set(file_paths).

A third is to check for both versions in credit_given() (125) and reported_news() (131).

I don't know if there is an issue with Macs or not.