Spring Physics - damping problem and plotting position

Hi all,

I’m trying to make a demo of spring physics with the integrated bullet engine.
Just a simple passive cube and a sphere somewhere below it, connected by a Generic Spring rigid body constraint, only in the z axis.
The Stiffness looks ok, but for me the damping does not look good. It looks like it damps the oscillation for the first couple of cycles but then remains with a practically constant oscillation without damping to rest as it should. Is this a known bug or am I missing something?

Another question is if there is any way to plot the sphere position over time, either in the graph editor or by baking it to an external file?