Ability bug?

[Sokar]

Being an assassin, the ability trainer has two similar abilities,
namely Adrenaline, and Assassin's Creed.

Adrenaline: (15000exp)
"Increases tactics by the greater of 20 or your dexterity / 10 for 25 minutes (30 minute cooldown)"

Assassin's Creed: (20000 exp)
"Increases tactics by the greater of 20 or your dexterity / 15 for 25 minutes (30 minute cooldown)"

The only difference seems to be the dexterity variable and experience cost.
But this makes no sense, as the more expensive ability would result in a lesser bonus.
Furthermore, this seems to not work.

I've tested with 300, and even 400+ dex, which should yield a 30-40 increase in Tactics.
However it never seems to go above 20, regardless of what dexterity is at.

I'll update if I find out more.