Bugged Or Arreat is wrong?
 

Well these are the stats for the stone runeword on arreat

Stone
4 Socketed Body Armor Shael + Um + Pul + Lum
+60% Faster Hit Recovery
+250-290% Enhanced Defense (varies)
+300 Defense Vs. Missile
+16 To Strength
+16 To Vitality
+10 To Energy
All Resistances +15
Level 16 Molten Boulder (80 Charges)
Level 16 Clay Golem (16 Charges)

And this is what i have.

Could it be that your item already had some %Enhanced Defense?, but im betting on arreat summit being wrong just so that I can dent there seemingly perfect image

oh i just remember the plate was a superior plate with enhanced defense.
Thx for clearing this out Gimbo :D

off subject question srry but what dose defence vs missile do?

Adds defense versus missle attacks (Arrows, etc..).

Would fireball be considered a missle?

Fireball doesn't require an Attack Rating roll, so no.

Nice def on armor, but pretty useless stats.