Got this and ran around a bit and it did go up. Zoned out and back in and it was back to the lower stats. Ran back upstairs to the camp and it didn't move at all. took it off and put it back on and stats are:
603 hp
640 mana
So it doesn't appear to have a memory of where you have been and you will need to run around all over again every time you zone into a different zone or even zoning back into the same zone. Too much of a pain in the *** for me especially being my mage is usually CoHing me all the time. I will stick with a more stable charm.