If you can't watch the videos, I group stuff and it starts... bouncing. That's the only word I have for it. It continues until I aim at them or switch to player mode.

I think it might be the confluence of the bug where stuff isn't properly selected after creating a group if you're not aiming at one of the objects in it (you have to go and aim at one of them, then it's all selected and able to be acted on) and the bug where creating a group sets all the objects in it to normal physics.

Whatever's doing it it's absolutely fucking magical. I wouldn't even be mad if it didn't keep happening when I'm trying to copy and rotate clumps of objects for my map.