annoying, pesky piece-meal raiders: please fix these, CA!

[Slaists]

This is the key IMO. How many units were you defending with? I guess that only few righ? Lets say two sepoys and one or two puckle guns. I assume the AI thought that it is enough to send a gun and one or two line infantry to defeat your meagre forces. When it failed it sent the same troops again, and again.
The problems are that (i) the AI obviously cannot learn, (ii) it cannot take into account human cunning and the dreadful siege AI.

Actually, this was an odd case (on my part), because I had a full stack of sepoys + green jackets (camping the houses) + light dragoons, even a couple pike-men to guard the gates. So, no... in this case, the force was not meager at all. Gibraltar was my choke point (gateway to Northern Africa) after all. Maybe just that the AI might count sepoys as mere milita...