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All these glitches are specific to your disk/downloaded game. Perhaps it's due to version 3.57.
(I'm talking about the number of harpies, experience resetting to zero, the commander not being able to be resurrected on level 22, and tower damage.)
As for the WOG development team, they only introduced errors in the war machines of parts 1-3. In the last part, if it's the tent's turn and you hover the cursor over an enemy standing near it, the game crashes 80% of the time. In the previous two parts, after a certain number of battles, the tents start running around the battlefield. I say it's their glitch because I found all these places in the code. It's impossible to do this by accident. It's clear that someone who didn't know what they were doing messed things up.
And all the errors that I've read about here, I haven't encountered even once. Even though I've played a lot. You can't even imagine how much.
+ I write maps and develop scripts for 3.58. There was plenty of time to notice anything.
P.S.: and regardless of the reason, all the glitches can be fixed. Go to the corresponding script and see what's wrong. Salnikov's team left plenty of comments, so it's not hard to find.