node-nanomsg: Pub/Sub stops after first message has been received.

I am absolutely new to nanomsg, so I might be doing something really stupid, but I can’t get this simple PUBSUB example to work:

var nano = require('nanomsg');
var addr = 'tcp://127.0.0.1:7789'

var pub = nano.socket('pub');
pub.bind(addr);

var sub1 = nano.socket('sub');
sub1.on('data', function (buf) {
  console.log('sub1:' + String(buf));
});
sub1.chan(['topic1'])
sub1.connect(addr);

var sub2 = nano.socket('sub');
sub2.on('data', function (buf) {
  console.log('sub2:' + String(buf));
});
sub2.chan(['topic2'])
sub2.connect(addr);

setInterval(function () {
    console.log('sending');
    pub.send("topic1 Hello from nanomsg!");
    console.log('sent');
}, 1000);

Running this gives me:

sending
sent
sub1:topic1 Hello from nanomsg!

And then there is nothing more (even if the node process does not exit). I would expect the setInterval to do this repeatedly, but after the first message has been received there is nothing more.

Any ideas? I have tried this on nodejs 5.11.0 on my Mac and on 6.2.0 on an Ubuntu machine.