I haven't opened the game for a few year now, but it's possible that this is a result of the physics engine which we kind of abuse to make certain things possible. We artificially create and apply forces to those parts and depending on how they are attached some unintuitive things can happen (if forces are big). This can also happen because the physics engine is not a perfect simulation and uses randomness for speed reasons.

This is not a good answer, but I hope it kind of gives a framework on how to think about the strange things happening in Nimbatus :)

Thanks and cheers,
Markus