Hmm, I really don't know why your CPU would be going up that much higher than what it's set to under load. I would try updating your BIOS (if you don't already have the latest rev), clearing CMOS, and reapplying your undervolt. Good chance it won't change anything, but it won't hurt. At the end of the day, there's nothing really wrong with the fact it goes up to 1.3V though.