When performing multi-touch gestures on Mac trackpad, for some touch points RELEASED is never reported. This causes death of scenegraph's multi-touch handling. The most reliable way to reproduce this is to perform the four-finger down-swipe which causes Exposé (while in the application). After that some of the four fingers are not released. When the next gesture starts, there are still some active fingers from the previous one which completely puzzles scenegraph. I think it is reproducible also by three fingers, but it's pretty hard and I'm not even sure about it.

Note that I introduced a workaround into scenegraph so right now it causes some minor slowdown but doesn't throw an exception. I will remove the workaround when this issue is fixed.