It looks like the alternative HUD draws three
values for each level statistic:
- individual value for the current player (multiplayer only!)
- value for the current level
- total value for the current level
i.e. how many kills/items/secrets you
have made/found personally, how many of them have been made/found in the current level so far, and how many of them are present on the current level in total.
In single player, the individual counters are absent, and they are the ones that get reset between map transitions. The level's current/total values do not get reset, I've just checked that myself. So I think this is not a bug, but rather an unimplemented feature - level serialization doesn't save individual statistics for each player.
(BTW, I didn't know these individual counters existed, might be a good idea to add them to my own mod too.)