Map Moddifiers Change the supposed to be Necro mods on the map

I did a few maps my self, tried putting 1 with scarab and one without both had different outcome of necropolis mods,
Today I heard that's not what it is, your map had a modifier ( variety monsters ) on it and changes the monster types and so at the same type the necropolis modifiers of it, but weren't the necropolis mods supposed to be the same for all maps for an hour.

Is this intended or is it a bug?