Animation cubic easing direction reversed

Cubic easing’s direction appears to be reversed when playing an animation on a Humanoid. For instance, according to this, with the “In” direction the motion should start slower at the beginning and become faster toward the end, however it actually behaves like “Out”.
This bug affects In/Out easing directions but not “InOut”, nor does it affect Elastic and Bounce easing styles. TweenService’s Cubic easing is not affected either.
This happens 100% of the time, both in Studio and in a live game, and both when playing it on a client or server; the old animation editor was also affected. The new animation editor behaves as expected, which results in the preview not looking like the final result.

CubicTest.rbxl (27.9 KB)

To reproduce the bug, just create an animation that uses Cubic easing in any keyframe, load it into any rig with a Humanoid and play it. Here’s an example:

Keyframe properties:
Playing the animation in-game:
Playing the animation in the editor:

As you can see, the animation editor works as expected, while the in-game animation doesn’t.


does this have any possible interaction with physics ?

You mean as in physics interfering with the animations?

yeah, is there ANY force at all, that could have an affect ?

I doubt it… I even tried on a custom rig with only two parts (one of them anchored, the other welded with Motor6D), and with Gravity set to 0 in Workspace. Uploaded the place in case you want to check it out:
CubicTest3.rbxl (23.9 KB)

Is there any way I could be absolutely sure?