Help With Castle Walls?

[Naja]

As we all know, there is a bug with Fortress/Citadel walls. If a unit can scale the first wall, that unit can reach the second and third wall without having to seige them.

The unit can travel through the wall's end to the beginning of the next inner layer of walls. It can also descend from the first wall and walk up a tower to ascend to the next layer.

In short, this spoils castles sieges. What use are the redundant walls and defenses? Even the AI exploits this, in both custom and campaign battles.

My question is, is there at least some temporary fix to the castle wall bug? Is there some code entry to 'disconnect' those upper wall layers from the lower layers?

Or, barring that, is there a way to make the AI not exploit the castle wall bug? Maybe an AI behavior that could be modified?

Thanks!