AI defending a town

First off I'd like to say this game rocks! I'm playing my first short campaign as the english on to unlock the russians who I'd really rather play. (I really hope they kick ass) which i'm doing instead of just editing the game files. My urge to unlock stuff probably a hangover from my console playing days.
I'd like to describe something that happened during one of my first siege battles. The defenders were rebels in a single wooden walled town having two longbowmen and three spear units as defenders. It being so early in the game I had only acsess to poor infantry so I assulted with 4 milita spearmen, 2 peasant archer, 4 mailed knights and a family member, foolishly expecting heavy casualties but still victory.
After being amused by my generals reference to the use of the works of Tacitus as toilet paper during the battle speech, I set my four siege towers to the walls manned by my milita spears. the long bowmen burned my two siege towers on the right flank just before they hit the walls. My spears on the left that reached the were met with spears units and melee from the longbowmen who were much better fighters than i expected. I threw my other two spears up the left towers to reinforce and my peasant archers on the empty wall area behind them with ladders. To my surpise the rebels reinforced the wall with the rest of thier spears on the ground( something the RTW AI would never do). My spears caused some casualties but when they all routed exected one who on the verge of breaking, as he held the enemy back from my archers who were practicly shooting blanks for all the damage they were doing and my cavalry sitting outside uselessly it became clear that the battle was lost. It was then that I had a cunning plan ("a plan so cunning you could pin a tail on it and call it a weasal" as Lord BlackAdder would say). I rushed one of my peasant archers off the wall and into the city square. with all the rebels on the wall now I easily started the final countdown just as the rebels started cutting into my archers still on the wall. The rebels rushed every man of them off the wall and to the square. With the wall now empty i ordered my battered archers to kindly open the gates for my 5 units of cavalry for some blood work. The rebels were in complete disarray after running pell mell in a long bee line for the square. They were quickly routed by a charge and the city was mine. :stupid:
In retrospect this might have been an unfair way of exploiting the AI but it was amusing to stumble upon a winning tactic in face of defeat.
Perhaps this needs to be patched? Having the AI always keep a reserve in the square(like in RTW) or having them send an adaquate force (rather than all) from the wall to retake the square.
In any case the battle was won, the city is mine and the dead cost nothing.