What would happen in the real world? If fully compact means full of material, then would corners have more material that would spill over after the turn? Or would this cause so much friction that materials would stop moving?
I think we need a mythbusters style investigation on this.
In the real world, the items aren't moving, it's the belt that's moving. So the belt just keeps spinning even if it's completely filled with items.
The cause of this bug is the fact that items move while the belt is static (despite the animation) and their moving requires a free spot in front of them. Once the belt is full, there's no empty spot for items to move into and the items stand still. The loop is stuck.
I think we need a mythbusters style investigation on this.