why does jeromq use setReuseAddress(true)?

I'm new to zeromq and not that experienced with sockets.

Are ZeroMQ sockets supposed to only allow one socket to bind() to a port?

The jeromq implementation allows more than one; pyzmq does not. Who's correct?

The jeromq ZMQ.Socket.bind() function eventually comes down to this:

https://github.com/zeromq/jeromq/blob/master/src/main/java/zmq/TcpListener.java#L141

//  Set address to listen on.
public int set_address(final String addr_)  {
    address.resolve(addr_, options.ipv4only > 0 ? true : false);

    try {
        handle = ServerSocketChannel.open();
        handle.configureBlocking(false);
        handle.socket().setReuseAddress(true);
        handle.socket().bind(address.address(), options.backlog);
        if (address.getPort()==0)
            address.updatePort(handle.socket().getLocalPort());
    } catch (IOException e) {
        close ();
        return ZError.EADDRINUSE;
    }
    endpoint = address.toString();
    socket.event_listening(endpoint, handle);
    return 0;
}

Python:

C:\tmp\jeromq\jeromq-0.3.2\target>python
Python 2.7.5 |Anaconda 1.9.1 (64-bit)| (default, May 31 2013, 10:45:37) [MSC v.1
500 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import zmq
>>> ctx=zmq.Context()
>>> s=ctx.socket(zmq.PUB)
>>> s.bind_to_random_port('tcp://127.0.0.1')
56356
>>> s2=ctx.socket(zmq.PUB)
>>> s2.bind('tcp://127.0.0.1:56356')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "socket.pyx", line 465, in zmq.core.socket.Socket.bind (zmq\core\socket.c
:4749)
zmq.core.error.ZMQError: Address in use

The jeromq implementation allows more than one

No it doesn't. Setting reuse-address on a TCP socket only fixes the frequent development problem that a listening socket can't be bound while there are connections to a prior instance of the application still in the TIME_WAIT state. It doesn't allow two instances of the port to be in LISTEN state.