On my MacBook Pro I can observe the following incorrect behavior for gestures. See attached demo program. (I can't say what the behavior
on other platforms is.)

When I move two fingers over the built-in track pad, I get the following kind of output:

setOnScroll: 0,000000 0,000000 1,000000 1,000000 0
setOnScroll: 0,000000 0,000000 2,000000 2,000000 0
setOnScroll: 0,000000 0,000000 1,000000 1,000000 0
setOnScroll: 0,000000 0,000000 1,000000 1,000000 0
setOnScroll: 1,000000 1,000000 1,000000 1,000000 0
setOnScroll: 1,000000 1,000000 2,000000 2,000000 0
setOnScroll: 1,000000 1,000000 1,000000 1,000000 0
setOnScroll: 1,000000 1,000000 1,000000 1,000000 0

The values are: e.getDeltaX(), e.getTotalDeltaX(), e.getDeltaY(), e.getTotalDeltaY(), e.getTouchCount()

This is wrong for several reasons according to the documentation for ScrollEvent:

1. The sequence of events for one gesture is never surrounded by SCROLL_STARTED and SCROLL_FINISHED.
2. The total-delta values are never accumulated. They seem to be the same as the delta values.
3. The touch-count is always 0. I'd expected 2 in this case.

This is also inconsistent with zoom events, where I get at least sometimes a zoom-started or zoom-finished notification. But this behavior is also not correct because it seems the zoom events are not surrounded correctly. Often I just get something like this:

setOnZoom: 0,998001
setOnZoom: 0,998001
setOnZoom: 0,994003
setOnZoomFinished
setOnZoomStarted

For rotation events the accumulation behavior actually works in contrast to the scroll events.

When I now attach an USB mouse to my Mac and create scroll events with the mouse wheel, the behavior is also wrong. The documentation says: "The totalDeltaX and totalDeltaY contain the cumulative values for the whole gesture, zeros for mouse wheel". As you can see here, the total-deltas for y are not zeros.

setOnScroll: 0,000000 0,000000 1,000061 1,000061 0
setOnScroll: 0,000000 0,000000 1,000061 1,000061 0
setOnScroll: 0,000000 0,000000 1,000061 1,000061 0
setOnScroll: 0,000000 0,000000 1,000061 1,000061 0
setOnScroll: 0,000000 0,000000 4,296417 4,296417 0
setOnScroll: 0,000000 0,000000 -1,000061 -1,000061 0
setOnScroll: 0,000000 0,000000 -11,195526 -11,195526 0
setOnScroll: 0,000000 0,000000 -38,627014 -38,627014 0
setOnScroll: 0,000000 0,000000 -50,805664 -50,805664 0
setOnScroll: 0,000000 0,000000 -52,142639 -52,142639 0

The current behavior is especially problematic for me because there does not seem to be any reliable way now to distinguish between mouse and track pad generated scrolling for which I have to take differnt actions.