mc_bin_client doesn't behave properly

If I do a get that involves a background fetch and an increment at the same time, both processes spin indefinately until I hit ^C at which point I get:

Traceback (most recent call last):
File "./binaryincr.py", line 6, in ?
mc.incr("someKey", 1)
File "/opt/NorthScale/bin/ep_engine/management/mc_bin_client.py", line 109, in incr
return self.__incrdecr(memcacheConstants.CMD_INCR, key, amt, init, exp)
File "/opt/NorthScale/bin/ep_engine/management/mc_bin_client.py", line 104, in __incrdecr
struct.pack(memcacheConstants.INCRDECR_PKT_FMT, amt, init, exp))
File "/opt/NorthScale/bin/ep_engine/management/mc_bin_client.py", line 87, in _doCmd
return self._handleSingleResponse(opaque)
File "/opt/NorthScale/bin/ep_engine/management/mc_bin_client.py", line 80, in _handleSingleResponse
cmd, opaque, cas, keylen, extralen, data = self._handleKeyedResponse(myopaque)
File "/opt/NorthScale/bin/ep_engine/management/mc_bin_client.py", line 61, in _handleKeyedResponse
response += self.s.recv(MIN_RECV_PACKET - len(response))