I have probably four or five cats that scratch the sides of the boxes instead of the litter to cover their stuff. I think it's amusing. Yes, they scratch a lot on the sides of the boxes. Oh well, they are kitties. Sometimes cats do things we mere mortals can't figure out. Maybe he is leaving the scent from the glands on his paws on the side of the box, therefore claiming the box as his, not Forests'.
Assumptions do nothing but make an ass out of u and me.
We can stick our heads in the sand for only so long before it starts choking us. Face it folks. The pet population is bad ALL OVER THE WORLD!