Ever since I moved my boys into the lower half of the DFN, their litter habits have been all over the place. If I put the litter box on the shelf, they will pee in it but not poop. If I put it on the bottom, they will poop in it but not pee. Since I didn't want to go out and buy another litter box just to test a hypothesis, I substituted a decent sized cardboard box with aspen and a couple of pee rocks. Now they have the litter box on the shelf and the makeshift litter box on the bottom. It seems to be working so far with no stray poops. They were fully potty trained even with their previous multilevel cage, I just don't understand the change, silly boys.