If a client disconnects sock.close() is currently never called because one cannot shutdown a not connected client:

Traceback (most recent call last):
  File "circuits/net/sockets.py", line 460, in _close
    sock.shutdown(2)
  File "/usr/lib/python2.7/socket.py", line 224, in meth
    return getattr(self._sock,name)(*args)
error: [Errno 107] Transport endpoint is not connected

This leads to still opened file descriptors/sockets in the procees:
python  20195 spaceone   10u  sock      0,6      0t0 11410688 can't identify protocol

If the server component runs for a longer time somehwen the open file descriptor limits is reached and your server is not able to react to any connection anymore:
Errno 105: No buffer space available