When a party member is hitting in melee an enemy, and this enemy decides to disengage, then party member starts chasing his target. This can be a real problem when party member was being engaged by multiple enemies, as he is going to take a disengage hit for each of them, sometimes killing himself by doing so. This can happen very suddenly and can ruin a fight in an instant

I think there should be a check implemented to AI so that a character does not chase an enemy that disengaged from him if he is still engaged with someone else. Instead, the character would automatically change its target and start attacking the remaining enemy or enemies he is still engaged with.

Iirc there are settings to the AI which should prevent this. 

You think it's because I had my party members set to 'Defensive' behavior that I had this happening ? If I put them to 'Defend Self', it may prevent this from happening ?

I don't remember the settings but I believe there was an auto-attack option that doesn't let party members chase enemies. Sorry, it's been too long and I didn't use AI much in the first place. When I come home I'd have to load up the game first to check.  

Yes, I agree with Boeroer, iirc there is a setting where you can set the companion not to chase their opponents, try to seek it

The "passive" setting should prevent party members from disengaging. 

Thanks for the answers. I thought about the 'passive' setting, the problem is the amount of micro-management that is then required ; it would be fine with a party of three, but six people feels overwhelming. I guess I could try to set only my frontliners to passive, and keep the range characters to the 'defensive' setting, that could balance things out