NHF – new heroes for Heroes V 3.1.

When does this bug usually occur? I read somewhere that it happens on the 1st day of the game.

It usually happens on a map with 8 players.
It doesn't always happen.
It's more noticeable on the 1st turn, then it sometimes disappears, and sometimes it doesn't.
It also disappears if you access the hero interface using a keyboard shortcut, but again, not always. And sometimes, it can be fixed for one player, but the bug disappears for everyone.