HoMM3 HD is a mod (add-on) for the game Heroes of Might and Magic 3.

Bug?
It seems that the hero doesn't necessarily have to enter the city menu to learn spells. If there's a city portal, they can do it from there. I think that's how it was in SoD.
Otherwise, you teleport, but forget to press the spacebar, and the spells aren't learned... That's not good.

In SoD, it was definitely always like this: in order for any of the city buildings to have an effect on the hero, you absolutely have to open the city screen. I know this for sure because I often "recharged" my mana in Dungeon on large maps using the Mana Vortex.

And today, I encountered a bug with a hero duplicate in the city for the first time! I was so surprised: I read that this bug was "long ago" fixed in the HD mod! But no. The mod version is 2.98.
Here's what happened: it's the enemy's turn in a single-player game, my hero is a guest in an allied city, where there's a small garrison of guards. The enemy attacks the city and captures it as if my hero doesn't exist at all! At the beginning of the day: I try to enter the city (it's already the enemy's), there's my duplicate without an army (I had a large one!), but with one Titan (the enemy obviously left it there for guard). I fight, the duplicate is defeated, and I get all its (that is, my!) artifacts, and my hero disappears! :(

I'm attaching the save file.