Unwanted movement on identical keyframes

[Toby from Shape]

Hi,
I have a project where I have a keyframed symbol where some parts of the timeline need to be motion tweened and others not. I achieve this by duplicating the segment following the motion tween and then unsetting the motion tween for the next segment. This all seems logical and a reasonable workflow.

If I adjust the length of the segment, sometimes - most times, the object jumps a few pixels when the timeline is moved onto a keyframe. If I check the transform values, they are identical, but there is movement - between .5 - 3 pixels roughly. 

This seems to happen more readily on keyframes that are rotated from their initial state on that first frame, but can happen on keyframes that have been completely default.

Any help much appreciated. 

[ClayUUID]

Is your animation so intricate that you actually need to be using motion tweens, or would classic tweens suffice?

[Toby from Shape]

Maybe, though I'm following a procedure laid out by a games company. There's some noises from them that it's just a thing with Animate, but I was hoping there's some best practice to avoid / minimise it. 

[Colin Holgate]

Could you make a small example FLA that shows the problem, that we can look at?