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

Medium_HP, I can't even imagine how HD could be doing this. Changes to the original code in HD do not affect spells and do not affect the contents of buildings in a town. As I understand it, a script is responsible for restructuring the GM in the WT. The HD mod does not make absolutely any changes to either the scripts or the WT script handler.

I have a hypothesis:
as a result of some unknown interactions between HD and WT,
Blindness becomes a prohibited spell for this town; if this is indeed the case, then at least we can't fix this bug at its root, but we can automatically fix this bug.

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I have already created a fix for the known types of hero duplication that I found, triggered by pressing a button. I will release an update for HD today or tomorrow.