Frostbringer is a weapon that lists 'AC: 7' among its stats.
http://wiki.project1999.com/Frostbringer
However, when equipped, it doesn't change your AC stat at all.
Observe these screenshots. The first one shows my character with Blade of Tactics in the offhand slot. This sword has 0 AC, and results in my character having 1428 AC.
edit.jpg
Now I swap out Blade of Tactics for Frostbringer. Frostbringer has 7 AC, but my character's AC remains as 1428.
edit2.jpg
As you can see, the AC on the Frostbringer is not being applied to my total AC. Thank you for your time.