If you put a VRC Parent Constraint on an object that is also controlled by a VRC Head Chop component, any children of that object that have avatar dynamics (physbones contacts, etc) will rotate, but will not move to the constrained location. The transform itself moves normally, but the avatar dyamnics themselves do not. This can be observed by viewing the debug overlays in game, or by trying to interact with the avatar dynamics. I can work around contacts by using another parent constraint to attach contacts as children, but for physbones there is no workaround. This is presumably caused by an issue with execution order, where the head chop is overriding the position instead of allowing the parent constraint to move it. This seems like a pretty big oversight because one of the main uses I can think of of VRC Head Chop is the ability to grab a hat off your head.