No, there haven't been any, either in the room that Jim and Sterling have shared with Foster Annie, nor in the rest of the house with the other 12 plus 2 of the foster kittens.
Now, does that mean that it IS behavioral? (it looks that way). But on the other hand, let's just think for a minute that Sterling has a medical problem (I am sure Jim's is behavioral and the medicine will help him). While Sterling is in a single room he has many litter boxes to choose from within a close walking distance (the 2 regular ones that are always in that room and one in each of the 2 cages that are still set up but the cage doors are open now). On the other hand, when I allowed Sterling out in the whole house the other day, he had much more space to cover. Even though there are litter boxes in every room, he might still have to travel farther to one than he would have had to if he were in that single room. That is why I think there could still be an underlying medical problem that we have yet to find.