Has anyone else noticed that their character’s Fortitude, Reflex and Will Saves will drop to –1 after a fight/damage?

My Wizard has started doing this since he got Greater Stoneskin and I added the 1.26 patch. Plus, it only happens if he takes damage in a fight (fails to duck or trips on a trap). He needs strip off all enchanted gear, I Quick Save and then I reload, he puts enchanted stuff back on and he is back to normal. Possible bug?