Remember that the spine is not on the surface of the back so any notation of spine position when the hips are not perpendicular to the view must be interpolated by other indicators like the position of the pelvis. Since 'Beachball effect' was your contribution I'd expect that you'd understand this.
Moe's hips do not move away from the target in frames after the second one in these clips and since the lower spine is connected to the pelvis it is safe to say therefore his lower spine does NOT return to it's address position.
It is also safe to say that due to 'beachball effect' surface markers on Moe's back would move away from the target as his hips rotated past parallel to the target line and since that is where you were marking in your analysis that is what you saw. But the spine is not on the surface even in a back view and surface markers do not mark the spine. With a little guestimation and math you can estimate how far off your analysis is vs the actual position of the spine with ever degree of rotation past perpendicular to the view due to beachball effect. Sine you contributed 'beachball effect' I'm sure you understand that and I'll leave it to you to do that math.