Hi! It seems Frostfury is bugged in a way.

When equipped, it deals less damage and has less thac0 bonus than a +2 axe.
Also, it's possible to notice Korgan has only 1 APR with it, while with Stonefire+2 (or any axe, really) he has 2 because of the 5 pips on axes.

It seems like my game isn't recognizing it as an axe, right?

I do have a mod that messes a bit with the proficiencies, add new styles etc, but every other axe and weapon seems to be working fine. My guess is that the weapon isn't flagged (?) properly.

I've tossed 2 screenshots of the axes mentioned above equipped just for a quick comparison here. 

And since I couldn't find a way to attach my weidu log, I've pasted it in this pastebin link.

Hope this is helpful!