This is probably a question for @msalsbery. I found another mouse tracking issue similar to openseadragon/openseadragon#626. On a touch device with an old, wired mouse, I found that I could get the image stuck to the mouse by doing mouse-down, touch-down, mouse-up, touch-up because no mouse-up event was fired. Using the device's trackpad, it was a lot harder to reproduce the issue--the device firmware was smart enough to fire a mouse-up event when I touched the screen--but I eventually got it into the bad state and through logging I could see that somehow it lost the mouse-up event while I was touching the screen. I can't see any reason why it should track the mouse at the same time as touch, so how does it sound if I add a patch to release all active mouse pointers on touch start?