[Autumn]

This isn't a bug, electric axe's on-hit is unresistable (meaning it bypasses DR). Body Guard's effect adds 50% DR when its effect triggers, which means it it wouldn't reduce the effect's damage.

Unresistable passes only Armor, Unprotectable means it bypasses both resistances and armor. Either way it is dealing unprotectable damage so the description needs updating (its probably just old), you are correct in that it should be ignoring DR.

More like either the description of the item is incorrect or the item is dealing unprotectable damage instead of unresistable and may be why Electric Axe is so unusually powerful.