You may want to ask the author about that one… I find it is quite glitchy on Safari of the time, but quite bizarre in how it affects Chrome when there is a physics body set to static.
The difference with physics is that there will be a heartbeat (requestAnimationFrame) constantly running and potentially setting element properties. I don’t know why this would affect the library which seems to rely on mousemove events. Perhaps less events are coming through when there is a constant requestAnimationFrame call? I don’t know.
What’s weird is that the cursor can seemingly move up and down more smoothly than right to left.