With an animation curve. e.g. transform.scale.x setting with a key set to 1 every frame. Changing this in the code will set it to the value in code, but it will not reset the value back to what it is meant to be in the animation.

Steps:
1. Open TestScene (Project: "AnimatedPropertyResetProblem copy.zip")
2. Press Play
3. Press A

Expected behavior: model does not stretch in x because animation has curves setting it to 1.
Actual behavior: observe that the model stretches in x, even though the animation has curves setting it to 1.

Other behavior (expected one):
1. Outside of Play mode, set "Turntle/Skeleton_GRP/root_JNT" transform.scale to any number other than 1,1,1
2. Press Play
3. Observe the scale gets set to that in the animation.
4. Press A as before (it will not stretch, animation setting it correctly)
5. Try modifying in the inspector, again will not change due to the animation setting it as intended.

Reproduced with: 2017.3.0a7, 5.6.3p2, 5.5.4p5.

BY DESIGN: This is intended. As scale transforms are constant curves in this instance, we do not re-evaluate the curve at every frame.