getTime() not working with Qt

Question

I have the following javascript code working fine in the browser but not in Qt:

var now = new Date()
var then = new Date("2013-12-08T00:10:01Z")
var timeDiff = then.getTime() - now.getTime()
alert(timeDiff)

When I run the same code in Qt timeDiff returns as NaN. Does anyone know why Javascript .getTime() is behaving differently in the Qt environment?

Update

Even the following is returning invalid date

console.log(new Date("2013-12-08"))

Might be related to the following question:

new Date("YYYY-MM-DD") stopped working in Qt WebKit after removing MacPorts

Note: I'm running the Qt on a BlackBerry 10 device hooked up to computer for debugging, not actually running the Qt program on my Mac.