I normally have an independent layer that I attach to the puppet (e.g. hair) and then put the dangle on the hair. That is, I don't put the dangle on the root object, but on the child independent object that is attached to the root.
In this example I had handy, the tie ("der") is independent and attached to the collar. The dangle at the bottom makes it sway relative to the rest of the puppet. If I put the dangle on the root puppet, it also starts locking down the root puppet. So I suspect "that's just how it works".
I have not used collisions and the particle system etc much, but to get a bouncing ball, I got some rectangles that I put just off the edge of the scene window and put the "collide" tag on them as well as the "ball" puppet.
There is also the Physics/Collide "bounce off sides" property, but I am not sure if that would work in your case or not.
Yes, the "bounce off sides" property works on the square, but not the "dangling" tail.
I expect that this is something that is not possible at this time because, probably, requires much more intense calculation, redrawing the mesh and so on.
I assume you put the collide tag on the tail layer as well. Did you try putting some rectangles on screen with collude as well? Probably won’t help, but worth a try!