In Vanilla Doom, if there are none of anything on a map, it will display 0% (i.e a map has no monsters, no items or no secrets).
In Vanilla Doom the counters also don't dynamically update mid map. Thus if any monsters, items or secrets are created/spawned mid map, the counter(s) will go over 100%.
Doomsday retains these behaviours (including in it's own in map counters), though some ports, like ZDoom change them. For instance ZDoom will display 100% in the case of a map containing no secrets and dynamically update it's counters mid map.
Of course, the OP might well be saying that they think the Vanilla Doom behaviour is questionable and in a way, it is (Heretic's intermission using numbers instead of percentages and hence displaying the likes of 0/0 secrets, is much more informative for instance).
If alternative behavior is desired then it should be requested via the proper channel. I wasn't aware that ZDoom has changed how those counters are displayed. Whether or not the ZDoom behavior is more intuitive is rather subjective, so it should be optioned if implemented.
Yes they are indeed calculated differently. The 0/0 => 0% on the intermission is a vanilla Doom behavior, whereas the percentages of the HUD cheat counters use 0/0 => 100% I wouldn't consider it a "bug" that the two behave differently, though. However, what you want is for the vanilla intermission behavior to be changed to match that of the cheat counter and so naturally this should be optioned and affect both displays (IMO).
Comments
In Vanilla Doom the counters also don't dynamically update mid map. Thus if any monsters, items or secrets are created/spawned mid map, the counter(s) will go over 100%.
Doomsday retains these behaviours (including in it's own in map counters), though some ports, like ZDoom change them. For instance ZDoom will display 100% in the case of a map containing no secrets and dynamically update it's counters mid map.
Of course, the OP might well be saying that they think the Vanilla Doom behaviour is questionable and in a way, it is (Heretic's intermission using numbers instead of percentages and hence displaying the likes of 0/0 secrets, is much more informative for instance).
and 0/0 i think it is 100%