The TreasureHunter (and a few other perks) are implemented by changing a global which is done from a quest (PerksQuest) from script fragment. But there's no code that revert that value in case the perk is removed by making the skill legendary for example. That global seems staying unchanged after you set skill to legendary or remove perk otherwise.

Is this known cause I can't find any reference with google? Anyone knows if USKP is fixing this?

How would you fix it for maximum compatibility as I don't want to edit any perk for this? IMO it would be an onPerkRemoved but we have no such...