I have to go through my history because I scoured the internet read hundreds of post on this but I believe Ralph Davis also has a leopard pied that throws all leopards.
It is my theorey that leopard is just the het form of a different line of pied. Think about ghosts you put a ghost with an orange ghost you get both even though they are different lines. So when you look at leopards if you took that line of pied and put it with the other you would get some of each line. So my thinking is these leopards put together makes your leopard pied, and since it only carries the leopard line of pied you will only get leopards when bred to a normal. If you make a leopard pied by putting leopard with the common line I believe you would get normal het pied when you breed it out