Thaumaturgical Infusion incorrect gem calculation

Hello. Faced a bug with floating 1-2 resists from ascendancy Thaumaturgical Infusion
Here I have shield with +2 to all elem resists and +3 to cold, and belt +5 maxfire. Also gems, lets's exclude green gems, in double weapon/spear skills they looks to be calculated as 0.5, doesn't matter.


So, from blue gems I should have +2 cold, and totally 75+5+2 = 82. But I have 81


If I take out 1 blue support gem (do it with shield support) and put it back, I will have correct 82


and same with red support. Reject/inject gives +1 to fire res, but lowers cold res



and finally reject/inject the green support just lowers both fire and cold by 1

checked with a shield without bonuses to max res and calculation is correct.
So, only shield with bonuses to max res gives such incorrect calcualtion