Two UDP binding operations to same port succeeds although expected to fail

Question

I'm listening to UDP messages by binding to a specific port and address using node.js:

var dgram = require('dgram');

var socket = dgram.createSocket('udp4');
var messageNumber = 0;

socket.on('message', function(data) {
    console.log('MESSAGE ' + (++messageNumber));
});

socket.bind(4353, '127.0.0.1');

The above code is able to receive messages, as I checked by the following sender code:

var dgram = require('dgram');

var socket = dgram.createSocket('udp4');
var address = '127.0.0.1';

setInterval(function() {
    socket.send(new Buffer('hello'), 0, 5, 4353, address);
}, 1000);

Now I'm starting another receiver while the first one is still running (using the same code above). I would expect one of the following:

• The second bind should fail (most probably).
• The second bind should succeed and both will receive the messages.

According to the following discussion the first option is the correct assuming node.js not using SO_REUSEPORT by default: Let two UDP-servers listen on the same port?

However what happens is that it doesn't fail, and only the last receiver gets the sender's messages. If I close the last receiver, the first one starts getting the messages again.

What's going on here?

EDIT: It seems that there are differences between machines. On Ubuntu machine I got the phenomenon described above. On Windows machine I got that the FIRST receiver gets the sender's messages (and again, when closing that receiver the other one starts receiving the messages). The common for both cases is that only one receiver receives the messages and the other one has no indication about that the port is in use (neither exception nor error - I tried also registering to "error" event).