Your cat may, however, be stressed, as this is a common cause of behavior issues such as a litter box problem. (cat-lovers-only.com)
Even if your rabbit has free range of your home it is important to provide it a cage as a safe haven or for use as a litter box. (hartz.com)
Perhaps instead, your own cat is the culprit, and is eating certain plants in your (or your neighbor's) garden or using the gardens as a litter box. (cat-lovers-only.com)