Haven't reproduced yet, but I'm fairly sure I know what caused it.

So the enemy attacked one of my patrols while I was near by and after the battle I got the dialogue from them as if I'd walked up to them to give them orders. I told them to go reinforce ismarla castle, since they where in no condition to fight, then where you would normaly get the capture/release dialogue with the lord(s) you just defeated I got the same dialogue set (as if I were talking to my patrol still)

Fearing messing the game up I just hit continue on the lords' diolague and was unable to capture them and try to use them as leverage to end my war, and give my estate some breathing room from this discord known as the caldarian wars.