logger interrupted

When there is heavy load (downloading tens of emails) I hit an issue with the logger:

[2015-07-29 16:58:45] DEBUG    - L#348  : leap.soledad.client.crypto:encrypt_docstr - Encrypting doc: M-2ffcba9f_6ff8_4988_8539_59d6f706a235-555130BA1B56D95E5E49C8BDA2BD0EF00CAE7FEAADF5EB4A0E975957D05C3389
Traceback (most recent call last):
  File "/home/meskio/bitmask/bitmask.venv/local/lib/python2.7/site-packages/logbook/handlers.py", line 217, in handle
    self.emit(record)
  File "/home/meskio/bitmask/bitmask_client/src/leap/bitmask/logs/safezmqhandler.py", line 118, in emit
    socket.send(json.dumps(self.export_record(record)).encode("utf-8"))
  File "zmq/backend/cython/socket.pyx", line 581, in zmq.backend.cython.socket.Socket.send (zmq/backend/cython/socket.c:5447)
  File "zmq/backend/cython/socket.pyx", line 628, in zmq.backend.cython.socket.Socket.send (zmq/backend/cython/socket.c:5209)
  File "zmq/backend/cython/socket.pyx", line 181, in zmq.backend.cython.socket._send_copy (zmq/backend/cython/socket.c:2048)
  File "zmq/backend/cython/checkrc.pxd", line 21, in zmq.backend.cython.checkrc._check_rc (zmq/backend/cython/socket.c:6261)
    raise ZMQError(errno)
ZMQError: Interrupted system call
Logged from file /home/meskio/bitmask/soledad/client/src/leap/soledad/client/crypto.py, line 348

It don't seem to block anything else, just the logs never arrive ~/.config/leap/bitmask.log. After a while reporting this error for every log line it fixes itself. Not sure if it happens only in this loggin call from leap/soledad/client/crypto.py.

(from redmine: created on 2015-07-29, relates #7234 (closed), relates #7569 (closed))