You best get Sylvia Brown AND Montel Williams over there, quick. Something going on in the paranormal.
If you make a habit of leaning back on that tank, even occaisionally, it will stress crack and break.
You have to remember that toilets are fragile and can break just under the strain of the tank to bowl bolts, the toilet flange bolts holding the toilet to the flange.
I replaced two toilets just this year, unexpected cracks.
I can see why the homeowner's warranty denied your claim. 1995 toilet, it's old and anyone leaning back on that toilet, even once could cause it to fail.