5* Kamala Khan green activation cost

While playing with finite (BRB &Polaris), I was surprised because I never reached 30 green AP.
After a while, I realised that the cost of the green power is paid after the power had it's effect. I do get 30 AP thanks to BRB, but the 7 from the activation cost are subtracted at the after the effect is done and damage has been dealt.
AFAIK, this is different from all other power, like 1* juggs in the same situation.
Is this a bug or a weird "as expected "?