Mac OS X pinch.center and pinch.previousCenter do not update

I run main.qml and use two fingers on the trackpad and slide them left or right while moving up or down. Trying to move the center point. It doesn't seem that the pinch.center value is being updated like a normal touchscreen would.

Attached is a modified version of the quick touchinteraction PinchArea example. Inside onPinchUpdated I added debug print statements for the values of interest.