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

You guys are really something. I also understand that playing with only one exit through a one-way passage is not ideal, and it's convenient without one-way passages. But is it fair to call the designers fools who didn't understand that one-way passages are an obstacle? It's just a bug, it's bound to happen... Following that logic, we should also remove the starting positions of Shakti/Valeska/Legion with only one stack, and the roads that take 4-5 days to traverse, and we could probably come up with many more complaints about the random map generator. But I thought that those who dislike randomness had long since switched to the World Tree.

Well, then, sorry, replayable auto-battles, bugs, and desynchronization are also part of the gameplay; remove the HD mod and play like that, you true SOD player.

I don't like the first point; it really changes the game. Bugs and glitches are not part of the gameplay; I hope I don't need to explain why.

Added 4 minutes later

Or is it also part of the game when the main hero goes down the first road into a one-way passage?

Generally, yes, even if it's not the most pleasant thing. I think using map templates with a reduced number of connections is a reasonable way to address this, and in general, 1-2 extra heroes usually solve the problem.