I've noticed a couple of small discrepancies between some weapons and the rest of the MEC they're attached to. Namely:
Arbelest's Shoulder Mortar's basic attack is Fin/Mob, but everything else on arbalest, including, the stratagem from the shoulder mortar, is Fin/Dur

The same is true of the Exorcist's Geist Sniper Rifle, which uses Dur/Com for its basic but everything else exorcist is Atu/Dur.

Was this intentional? are these typos? I ask because it's kind of getting in the way of my sniper witch build.

These are both typos! ((Thank you for catching this)) Usually when you see those it's something escaping find/replace. Also very excited to potentially hear more about your Sniper Witch build >.>