This is a very minor bug and thus should be easy to fix I guess.
If you have at least one of the lucky numbers heavenly upgrades (Lucky Digit, Lucky Number and Lucky Payout) that allow your prestige level CpS multiplier to exceed 100%, your prestige multiplier will be correctly displayed in the Stats tab but not in the Legacy tooltip, as exemplified here with only one of the three update (tested on a Game.RuinTheFun() tab as well).
Also this is not a bug but rather a minor complain on my end, I believe that there should at least be a hint as to how to unlock these three heavenly upgrades, because it pretty much comes down to luck if you don't already know about them. Not every player looks up the wiki or checks out a Game.RuinTheFun() tab on every update, and even if you were to unlock the first one by chance (which is actually pretty easy, there's a 10% chance of that), it's very unlikely that you'd even know that there are more than one of these hidden upgrades. I dunno, minor complain as I said.