Spoiler ahead (this is why I didn't put the character names in the title).

Corgan and Selina attack and when they don't miss, they either make damage (>0) or they don't (=0). Does anyone know the reason of this? If this is a bug, why is it only appearing with these two characters? I tend to kick them out of my party, when I have the chance, because I think this is really annoying.

well, I checked it and you are right. The same kind of attack can miss or does 0dmg. I got the same issue with at least one more hero (dont remember who).
Anyway it doesnt bother later while your percentage to hit is quite enough