spirit bug on minion skill

Frozen Mandible has original spirit cost 99
passive skill: lord of horrors reduce 12%
2x talisman of Ralakesh on helmet reduce 12%, why the final cost to be 80??

lord of horrors reduce spirit 99x12% =11.88, this game just removed the .88 to get final cost at 88.

but 2x talisman of Ralakesh on helmet provide 12%, how come get 80.

99x24%=23.76 which is reduce 23 spirit =76

or 88x12%=10.56 which is reduce 10 spirit =78, how come to get 80.

Summoning Class build mostly higher and spend more time on game.
if GGG doesn't want people to play any build with minion, just remove all of them to save player time to spend time on POE2.