Muslims king of Jerusalem?

[Nviard55]

I play with project balance (unhistorical empires removed with SWMH and NRBT+).
I just found out a strange outcome in my current game when the Fatimid Caliphate launched a jihad on the Kingdom of Jerusalem circa 1168.
The Fatimid caliphate won, conquered the kingdom of Jerusalem. Right after that they destroyed the Caliphate and chose Jerusalem as their main title instead.
The former king of Jerusalem (Amaury of Anjou), now only Duke of Acre, along with the Count of Tripoli and the Prince of galilee bent the knee and are now vassals to that muslim kingdom!?!
And even worse, the templars and hospitaliers are also vassals to the muslim king of Jerusalem. Doesn't make sense to me.
Is it normal? Anyone else ever experienced such WTF outcome after a war or is it a bug?

 

[aliates]

I think muslims can't form the KoJ but can usurp it, which is still problematic as it leads to the funky stuff you mentioned. should never be able to usurp it OR have it auto-destroyed when usurped (giving some prestige instead of the ususal prestige loss you get for destroying titles)