Meg, I'd crate him & Gracie for a week or so, unless you have a small room somewhere without carpeting. Being that he only sees shadows, maybe he's losing track of where the litterpans are. When they were here, I kept them crated while at work, and let them out for the rest of the day. They'd always follow me downstairs where there's lots of litterboxes, and I'd often see them using the big potties. You can't let it become a habit with Gabe at this stage, so I'd definately lock them up for a week at least until this behaviour stops. If there's specific spots he's pooping in, use straight vinegar on those areas, and leave a shallow bowl with more in it to discourage him from that area. I hope this helps.