From memory, and from some searching around, at some stage in the hunger cycle HP should stop regenerating. 3 hours for normal races and 1.5 hours for the fast matabolizers. Currently, only the stamina regeneration component of the hunger cycle is working on P99.
Steps to replicate: made a level 1 halfing, deleted starter food/drink, waited over 3 hours. HP still regening.
Source:
http://web.archive.org/web/200010112...ing/food.shtml