node.js cluster kill

cluster-sig.js

var cluster = require('cluster');

if (cluster.isMaster) {
    cluster.fork();

    cluster.on('exit', function(worker, code, signal) {
        console.log('Worker exited:', worker.process.pid);
    });

    setTimeout(function () {
        for (var id in cluster.workers) {
            var worker = cluster.workers[id];
            worker.kill('SIGUSR2');
        }
    }, 2000);
} else {
    process.on('SIGUSR2', function() {
        //WHY DOES THIS NOT GET CALLED? http://nodejs.org/api/cluster.html#cluster_worker_kill_signal_sigterm
        console.log('SIGUSR2 called', process.pid);
    });
    console.log('Worker listening for SIGUSR2', process.pid);
}

it's very interesting that

worker.kill('SIGUSR1');
worker.process.kill('SIGUSR1');

did completely different things for me as i was probably trying the same thing above.
and the 2nd would actually work as expected:

worker:11380 listening!
Hit SIGUSR1 - starting debugger agent.
debugger listening on port 5858