Removing layers from the control does not restore them to both sides

[RacingTadpole]

This is a very handy control - thanks for developing it!
I'd like to be able to add multiple layers to either both sides, the left side and/or the right side - and then shift them around between sides.
This mostly works, but when a layer is removed from the side-by-side control, its clip property is not removed, stranding it on whichever side it was on, and not updating when the control's position changes.
I have some changes which should address this, which I'll submit as a PR.