Logged In: YES 
user_id=185428

(1) I think it is a problem because under Mac OS X the user
#2 sees "sub2" (and not "sub1"!) as the working directory,
which is where it is different from Linux.

(2) The problem persists even if all permissions are open.

(3) The implementation of "os.readlink" migh be the right
clue about the problem: when the user #2 executes
"os.readlink("/Users/owner/TESTPATH/sub2/testpath.py") the
answer under Mac OS X is:

OSError: [Errorno 13] Permission denied:
'/Users/owner/TESTPATH/sub2/testpath.py'

even though all permissions are open.

Under Linux I get the expected answer: "../sub1/testpath.py".

Obviously there is a problem under Mac OS X, and this matter
should be reopen.