Bluebird.js custom Error catch function, does not apply on the first promise?

I'm trying to use the custom error handlers of Bluebird.js. In the example bellow the catch-all handler is called, not the MyCustomError handler, but when I moved the rejection into the then function (and resolved the firstPromise...), the MyCustomError handler is called. Why is that? got something wrong? Thanks. ``` var Promise = require('bluebird'), debug = require('debug')('main'); firstPromise() .then(function (value) { debug(value); }) .catch(MyCustomError, function (err) { debug('from MyCustomError catch: ' + err.message); }) .catch(function (err) { debug('From catch all: ' + err.message); }); /* * Promise returning function. * */ function firstPromise() { return new Promise(function (resolve, reject) { reject(new MyCustomError('error from firstPromise')); }); } /* * Custom Error * */ function MyCustomError(message) { this.message = message; this.name = "MyCustomError"; Error.captureStackTrace(this, MyCustomError); } MyCustomError.prototype = Object.create(Error.prototype); MyCustomError.prototype.constructor = MyCustomError; ```