If an object, which as been put() in the multiprocessing.Queue is changed immediately after the put() call then changed version may be added to the queue which I assume is not the expected behaviour:
>>> from multiprocessing import Queue
>>> q = Queue()
>>> obj = [[i for i in xrange(j * 10, (j * 10) + 10)] for j in xrange(0,10)]
>>> q.put(obj); obj[-1][-1] = None
>>> obj2 = q.get()
>>> print obj2[-1][-1]
None
Note: This also happens if the queue is called form a child process like in the attached example.