Configuring Browserify with factor-bundle and watchify

Question

I am trying to configure my application to use browserify with watchify and factor-bundle. However, I seem to either end up with a memory leak or break watchify triggered builds.

My build.js

var browserify = require('browserify'),
    watchify = require('watchify'),
    fromArgs = require('watchify/bin/args'),
    fs = require('fs');

var inputs = [
  './client/src/application.js'
];

var outputs = [
  'app/assets/javascripts/bundles/application.js'
];

var commonOutput = 'app/assets/javascripts/bundles/common.js';

var bundle = function(b){
  b.plugin('factor-bundle', { outputs: outputs });
  b.transform('browserify-shim');
  b.bundle().
    on('error', function(err) {
      console.log(err.toString());
      this.emit('end');
    }).
    pipe(fs.createWriteStream(commonOutput));
};

var watcher = watchify(browserify(watchify.args));

watcher.add(inputs);    
watcher.on('update', function(ids) {
  bundle(watcher);
  console.log('updated with ids:', ids);
});

watcher.on('log', function(msg) {
  console.log(msg);
});

bundle(watcher);

With this configuration I get eventually get:

(node) warning: possible EventEmitter memory leak detected. 11 listeners added. Use emitter.setMaxListeners() to increase limit.
Trace
    at WriteStream.EventEmitter.addListener (events.js:160:15)
    at Labeled.Readable.pipe (/Users/bmcmullen/dev/whitepages/fouroneone_line/node_modules/factor-bundle/node_modules/labeled-stream-splicer/node_modules/stream-splicer/node_modules/readable-stream/lib/_stream_readable.js:527:8)
    at /Users/bmcmullen/dev/whitepages/fouroneone_line/node_modules/factor-bundle/index.js:73:43
    at Array.reduce (native)
    at Transform._flush (/Users/bmcmullen/dev/whitepages/fouroneone_line/node_modules/factor-bundle/index.js:65:35)
    at Transform.<anonymous> (/Users/bmcmullen/dev/whitepages/fouroneone_line/node_modules/factor-bundle/node_modules/through2/node_modules/readable-stream/lib/_stream_transform.js:135:12)
    at Transform.g (events.js:180:16)
...

I assume this is because I'm creating that write stream each time and the old ones are not being collected? But I can't figure out the right way to do it.