Spellsword perk's DR bonus is removed after an overriding DR bonus is removed

[Eraamion]

So, a sorcerer with the spellsword perk and its 5/+1 DR casts stoneskin on himself, which overrides the perk. The stoneskin goes away but the default spellsword DR also went away. Needs relogging, resting or resetting the perk for it to return. The stoneskin tends to go away during heavy melee, so suddenly finding yourself in battle, unarmored and without -any- DR can be very deadly.

[Talir]

Are you sure you were not facing an opponent which can pierce x/+1? Effects do not go away like that.