In three battles now I saw the AI behave herself very strangely.
First of all was in a battle with Armenia against the Turks. I had about 2000 men and the AI came with 3 armies on the battlefield. Each of them about 2000 to 2200 men.
I annhilated the first army and lost more then 1 third of my army. (thx to their horsed archers...) And then the other two armies didn't advance. They could have broke me in a few mins but they didn't move a quarter...I won the battle (since I was the defender) after the clock run down.
I had a similar battle with the Scotts against the English and now another one with Byzantine againt venice...