Queuing the class doesn't do anything here. It gets pickled as a module attribute; the queue isn't marshaling the class dict. For example:

    >>> pickletools.dis(pickle.dumps(mccabe.McCabeChecker))
        0: \x80 PROTO      3
        2: c    GLOBAL     'mccabe McCabeChecker'
       24: q    BINPUT     0
       26: .    STOP
    highest protocol among opcodes = 2

Unpickling this is basically getattr(sys.modules['mccabe'], 'McCabeChecker'). So you'll see the same result if you only put ('max_complexity', 10) in the queue and hard code the class in the _target function. 

Of course for a system that uses fork() the class attribute is the same in the child process. In 3.4+ you can force spawning by initially calling multiprocessing.set_start_method('spawn'). Then you'll see the same result as in Windows.