* For one of my test characters the Stormcloak Stone also enhanced the Imperial Armors. Have no idea what caused it. 

* Occasionally some of the armors (especially helmets) 'remember' the Stone even if you have changed your Stone
to another one. The bonuses wear off only when you unready ALL armors of the same type (Imperial or Stormcloak). This probably has something to do with either the inventory UI or how I implemented the actual enchantment in Creation Kit.