ZombieJS problem or JSDom bug?

[mrft]

browser = new Browser( { site: "www.boechout.be", waitDuration: 30 * 1000 } )
browser.visit( "/eloket/default.aspx", function( err ) { ... } )

prints the following error message (causing javascript trouble later on)

node_modules/zombie/node_modules/jsdom/lib/jsdom/events/EventTarget.js:40
  if (handlers.indexOf(callback) !== -1) {
              ^
[Error: Cannot read property 'indexOf' of undefined]

The thing is, it is definitely a problem happening in EventTarget.js, but I don't know what is causing this, and if it is a jsdom bug or a zombiejs bug.

If it's a jsdom bug, I wouldn't know what information to give them so they will understand the nature of the problem.

Can anyone give me some clues to help me understand what's going on (or maybe a fix or a workaround?).

(Is there a way to get more detailed information about when and where the error happens? So that I can see actually what on that page is causing the problem, like is it an external javascript library on that page, and if so which one, and what line of the code is causing it?)