In most D&D games, hit points gained on level-up is a hit die (d6 for casters, d8 for rogues and clerics, d10 for warrior classes) roll + constitution modifier. The roll is usually made when the level-up is selected. This means that "save before leveling up and reload if you don't like the roll" is a valid tactic in single-player games. Here, however, reloading the save seems to do nothing, and I keep getting the same post-level-up HP, and what's being selected is neither the maximum roll nor even an average. It's not a big deal since the roll isn't terrible, but I'd like to know how it works.

Does anyone have any idea what's going on?