But I'm telling you, that has never happened to me once in all the time I've played Civ 4, and I've played it for many years.
It must be removed on Settler difficulty.
That's the only way I wouldn't have noticed it once.
It sounds like it was designed especially for Deity level only.
You know, where you as the player can't win.
If I have ever lost XP, I just never noticed it, or it was 1 XP, and I gained it back later. Or I only upgraded my units at something they wouldn't be reduced from.
I've upgraded Macemen to Infantry. Or maybe Riflemen, and they still have the exact same XP.
I've turned Calvary into Helicopters. and they stay the same XP. Or maybe that was a Rise of Mankind only thing. I did it in that mod.
Maybe I am the victim of the most awesome bug ever?
The bug that prevents that from having an effect?
Okay, my new game has a really glitched out map.
I entered world builder to see why there were so many animals near my city, and according to world builder, every tile of the map had an animal.
Maybe not exactly every tile, but every tile within 30 of my capital city outside my borders had an animal.
Might want to reduce the spawn rate of animals.
I don't know what happened, but compared to my last game, this is a bit silly.
I'm pretty sure Settler difficulty doesn't allow 180 animals to spawn at one time.