Comment 6 for bug 805972

Here's some notes from my investigations:

* It is only reproducible on a full multitouch trackpad, which currently are only Apple trackpads
* There seems to be some smooth scrolling and then a snap reversion
* On a touchscreen, two touch drags produce inconsistent smooth scrolling but no snap reversions

This leads me to believe there is some code in the Qt scroll view class that subscribes to two touch drag gestures from Qt. Qt has its own gesture recognizer that is not hooked up to uTouch, though that's beside the point. The trackpad issue can be explained by the scroll view performing smooth scrolling for a bit and then snapping back when an X scroll event (button presses 4, 5, 6, or 7) is received. Touchscreens don't emit X scroll events, so there's no snap reversion in that case.

I don't trust the Qt smooth scrolling based on what I see when using a touchscreen. It's not a 1:1 scroll and it often doesn't work. Our best course of action for now is to patch out the gesture subscription from the Qt scroll view class.