Mouse events seem unstable, as if we are getting occasional erroneous values, causing storage behavior on BrickBreaker and Ensemble. Igor took a look at it and his thinking is that the events are sometimes not getting mapped back into coordinates that are relative to the browser window, but are being delivered in absolute screen coordinates. I think this is a good working theory.

BrickBreaker.html
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One time, the animation stopped and no more updates happened.

Sometimes the paddle jumps around when you move the mouse

Ensemble.html
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No mouse event handling, after third try it worked, but the mouse pointer was "off" in Y initially.