War machines in Heroes V.

Has anyone else experienced this? It happens after a few turns, and it creates a stalemate where the attacking side is forced to retreat and engage in open battle.

I haven't experienced it myself. I was just thinking about what would happen if it did. In that case, you'd have to rely on flying units. But if you're besieging Inferno and there are a lot of demons, even the Earthquake spell won't help the attacking hero. The defense would involve pushing units through the walls by opening portals.