Your problem sounds very familiar. I would guess that the defrost water drain line is plugged or frozen, so that the drain water has no place to go except to the bottom of your freezer. In time the drain water would leak out on to the floor. There are several threads on this forum concerning the same problem & fixes. My KitchenAid requires a replacement part in the drain line, which KitchenAid has offered to replace at no cost to me. Good customer service !
Roger