So, in order to fool Bongo to accept object which is being part of the animation hierachy not at first, and let it become a “child” to another rotating object only after the motion has begun, I had to fake it by using two objects (2 coils), one which is moving towards a rotator object and when reaching its position it’s immediately hidden, and at the same time another copy of the coil is shown (from being hidden before this point in time). If stepping the KeyFrames manually it works, but not when starting the animation with the Play button.
Fig 1. The animation shows manual stepping at first, then repeats in play mode (this time the coil doesn’t show up - around frame 000030 the second time - when the rotation sequence starts again):
I think this bug has been reported before. The trick I’m trying above is the only way I know of to fool Bongo to take on (connect) a child object during animation.