What has happened to AI doing full retreat function in battle (not in campaign map)?

[ntabc2001]

Because of nostalgia, I decided to play Rome TW again few days ago. I remembered, but, somehow, I didn't pay any attention, the AI can plan, and do a full retreat, very frequently.
This is the battle they did the retreat:
_ Me: Rome, 4 hastati, 1 general bodyguard
_ AI: Gaul, 1 swordmen, 1 warband, 1 gallic horsemen (general is in this unit, not Family Member).
_ AI retreated when swordmen, warband got toast, I failed at catching those horsemen, only gallic foot soldiers were caught.
,and some others battles, you know...

Also, I vividly remember in M2TW, AI did do some retreats, I'm going to play a Stainless Steel and a vanilla campaign, personaly test it out.

My question is what ever has happened to that function, I can't find any related thread on google about this subject, my bad maybe, so if anyone find anything, post here for me to read.

[OwainKGB]

I don't think I've ever seen the AI retreat other than after I triggered a rout in regular engagements. I see it frequently in in sieges though, particularly if all the AI has is a battering ram. If I destroy the ram, the enemy just turns tail and runs. If I sally forth from the walls with a strong force, the AI will back up and reform. Once I've formed up and start advancing, if I out number them, they'll also frequently head for the hills.

[z3n]

I've seen it once or twice but it's very rare. I believe they need to be able to retreat in the first place (have movement points remaining and did not retreat once before on the campaign map).