Just a few questions:
How many litter boxes do you have for all 7? The rule of thumb is 1 for each cat plus 1. I know that may be a little extreme, but there should be at least 3 or 4 boxes.
Are all 7 cats exhibiting this or just 1? When a cat stops using the box, it could mean a medical problem.
Some cats like to urinate in one box and have bowel movements in another box.
Also, with multiple cats, having different boxes eliminates the ambushing while others are trying to do their business.
Please let us know!