mbrestore displays python interrupt.error when running without -a option

Exception in thread Thread-1 (most likely raised during interpreter shutdown):
Traceback (most recent call last):
  File "/usr/lib/python2.6/threading.py", line 532, in __bootstrap_inner
  File "/usr/lib/python2.6/threading.py", line 484, in run
  File "/opt/membase/lib/python/mbrestore", line 91, in worker
<type 'exceptions.AttributeError'>: 'NoneType' object has no attribute 'interrupt_main'
membase@ubuntu1004-64:/root$ exit