First of all I'm a programmer not an animator so maybe I'm not following why this would be the case (if that's so please explain it to me! π) But I'm seeing behavior with animation interpolation that I don't expect. Below is a gif of two animations being played back and forth and the resulting interpolated position shown by a sphere. The text shows the bone's position in world space as well as which animation is currently playing.
It's a very simple test. The bone is placed high during setup and for both animations is placed immediately, on the first keyframe, out to the right in the same position. When interpolating between the animations we see the sphere move back towards it's setup position (exactly 25% the way there at the midpoint, almost like having 2 50% transparent images resulting in 75% opacity). My expectation of this behavior is that since the sphere is set to the same position on the first frame for both animations is that the interpolation would between two same values and result in no movement.
We see this on more than just bone position. If we have an ik constraint set to 100% on the first frame on two animations and interpolate between them it'll go to 75% and back within the interpolation duration (causing noticeable hitches).
Thanks for any info!
C.J.