Demon invasion.

I started playing the updated version of the campaign and noticed something – I don't know if it's a bug or not. I captured the first Dwarf castle, Khrottar, and for some reason, none of my heroes interact with it. I can build in it, I can hire heroes in it, but when I enter the castle, the heroes don't appear. It's strange, and as a result, I can't learn spells in it. Has anyone else encountered this? Is it a bug or a feature? (I don't have any third-party mods installed; I'm using a clean version of 3.1). I can enter the city using the "Portal to City" spell, but the heroes don't appear in it when using the normal method.