My program doesn't have bugs. It just develops random features.
The return group this mover belongs to. All movers in a return group form a linked list of "followers" with each mover's Leader pointing to the main mover that should be triggered, bumped, or otherwise activated. The leading mover will tell its Follower to open/close whenever it opens or closes itself. The follower in turn will do the same with its own follower, and so on. Make sure only one mover in a return group is flagged as the leader, otherwise you might experience weird stuff including "Infinite Script Recursion" crashes.