assertion failure on socket disconnect

While trying to diagnose a connectivity problem with a customer server, I had a pymongo client connected to one of our servers with ssl=True and use_greenlets=True, just sitting with the idle connection open, logging the date/time and the return value from connection.alive() once a minute. After about 9 days there was a disconnect but I think that may have been caused by us on the server side. The client side result was an assertion failure:

Traceback (most recent call last):
File "test.py", line 11, in <module>
print (time.ctime(), c2.alive())
File "/usr/local/lib/python2.7/dist-packages/pymongo-2.6_-py2.7-linux-x86_64.egg/pymongo/mongo_client.py", line 852, in alive
self.__pool.maybe_return_socket(sock_info)
File "/usr/local/lib/python2.7/dist-packages/pymongo-2.6_-py2.7-linux-x86_64.egg/pymongo/pool.py", line 397, in maybe_return_socket
assert sock_info not in (NO_REQUEST, NO_SOCKET_YET)
AssertionError

I can try to reproduce this if you want, by pointing the client at a test server and then stopping the server, but I thought maybe the above is enough to be useful.

Output of pymongo.version is "2.6+" but I'm not certain of the exact build.

Paul