Unfortunately, I couldn't find a "clean" version of the Tribes of the East anywhere. I downloaded a bunch of different versions from torrents and tried them all. The bug is present in all of them. I tried deleting all the maps from the maps folder and the mods from the usermod folder. In different versions, there are still non-standard maps in the list, and the bug doesn't disappear. In general, it's not clear how to fix it, and the most interesting thing is that I'm not the only one playing these Heroes of Might and Magic builds, and no one has written about the problem.