Class Hall mission percentage calcualtion is wrong

[Alcesto]

WoW Freakz link:
Bug description: Game wrongly calculate mission critical chance percentage based on followers ilvl and items. On this particular mission, i have cumulative 245% succes chance. You can see it on the screenshot below. After choosing this mission, i got 145% result.
Proof: https://imgur.com/a/JXWK2lR bonus items wiev
https://imgur.com/a/izyjJKP final succes chance
https://www.mmo-champion.com/threads/2126985-order-hall-Champion-Stacking-Buffs

From left to right:
+20% from first mission of the day,
+10% from Assassination
+20% from Sturdy Hiking boots
+30% from Bottomless Flask
+10% from Lucky Doodad
+30% from Bottomless Flask
+20% from Sturdy Hiking Boots
+40% from Vial of Timeless Breath

Buffs not seen, but also should be added
+15% from Garona Helforcen Master Assassin
+15% from Lilian Voss Soulsever Blasde
+10% for each Follower doing mission
base 5%

Looks like, if 2 of the same items are present, like in this case 2x sturdy Hiking Boots and 2x Bottomless Flask, added % from those items are canceled. In this case -40% and -60%
As you can read in this thread: https://www.mmo-champion.com/threads/2126985-order-hall-Champion-Stacking-Buffs, all should be counted cumulatively.