BlobManagerTestCase.test_send_missing fails randomly

I get this sometimes, but i can't identify conditions that make it fail:

========================================== FAILURES ===========================================
____________________________ BlobManagerTestCase.test_send_missing ____________________________

result = None, g = <generator object test_send_missing at 0x7f4e37c6baa0>
deferred = <Deferred at 0x7f4e373fe440 current result: None>

    def _inlineCallbacks(result, g, deferred):
        """
        See L{inlineCallbacks}.
        """
        # This function is complicated by the need to prevent unbounded recursion
        # arising from repeatedly yielding immediately ready deferreds.  This while
        # loop and the waiting variable solve that by manually unfolding the
        # recursion.
    
        waiting = [True, # waiting for result?
                   None] # result
    
        while 1:
            try:
                # Send the last result back as the result of the yield expression.
                isFailure = isinstance(result, failure.Failure)
                if isFailure:
                    result = result.throwExceptionIntoGenerator(g)
                else:
>                   result = g.send(result)

.tox/py27/local/lib/python2.7/site-packages/twisted/internet/defer.py:1386: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
tests/blobs/test_blob_manager.py:119: in test_send_missing
    self.assertEquals('test', call_fd.getvalue())
.tox/py27/local/lib/python2.7/site-packages/twisted/trial/_synctest.py:432: in assertEqual
    super(_Assertions, self).assertEqual(first, second, msg)
E   FailTest: 'test' != '\x00\x00\x00\x00'
!!!!!!!!!!!!!!!!!!!!!!!!!!! Interrupted: stopping after 1 failures !!!!!!!!!!!!!!!!!!!!!!!!!!!!
============================= 1 failed, 7 passed in 6.00 seconds ==============================
ERROR: InvocationError: '/home/drebs/dev/leap/repos/soledad/testing/.tox/py27/bin/py.test -x --ignore=tests/benchmarks --cov-report=html --cov-report=term --cov=leap.soledad -v -x'
___________________________________________ summary ___________________________________________
ERROR:   py27: commands failed