Going from 2.1.4 to 2.1.6 has been an utter disaster for me. Relatively simplistic TCP communications between processes give me a never-ending stream of:
Assertion failed: (msg_->flags | ZMQ_MSG_MASK) == 0xff (zmq.cpp:223)
Assertion failed: rc == 0 (zmq_connecter.cpp:48)
Trying to connect to a server running 2.1.6 from a client running 2.1.4 will also kill the server.