3rd order acceleration (jerk) behaves weirdly

[ssylvan]

See terjeio/ioSender#482

First, it seems pretty strange that any amount of jerk compensation should lead to this slow stopping. Maybe there should be some sort of minimum acceleration where you just stop smoothing jerk below that (at least when stopping).

Second, any jerk smoothing should be disabled during EXEC_MOTION_CANCEL_FAST surely?

[terjeio]

It is likely related to a known issue. See this comment.

[ssylvan]

Seems likely. The second part is a little different though - during a cancel operation we should presumably just stop the steppers immediately and ignore any acceleration or jerk limits?