Antax Mk V Combat Axe heavy attack bugged?

When doing the heavy attack on that axe, it will do less damage than a normal attack to specialists/maniacs (flamer, sniper, dog, trapper, mutant, rager) ONLY. Everything else seems fine.

Repeat this only seems to be a problem on the specialists. Does anyone else have this problem?

Axe stats. 309
+25% damage maniacs
+8 melee crit damage

Decimator +8% on hit 5x
Headtaker +4% power 3.5s 5x


Ye something weird is going on.

Light attack: 1023
Heavy attack: 641

Light attack: 300
Heavy attack: 180

Light attack: 1023
Heavy attack: 556

Light attack: 246
Heavy attack: 186

But seem to be the same on other axes aswell that i tried on.