If a UI item is inadvertently placed on top of another (or spawns there), there is no way to unstack them. Attempting to move the UI item that is on the top of the other will move both, and they will be stacked permanently from then on.
reported by https://github.com/Swivelgames
migrated from https://github.com/OpenMusicKontrollers/patchmatrix/issues/28