Something happened I don't understand. My heir came of age and was listed as "unassigned." I decided I wanted him to command a horse archer unit, so I shut off all; troop production for a season, except one horse archer. He was not assigned to that unit. So I tried again next season. Same result. So just to see what happened, I made only YA's for a season. Still no assignment. In the fourth season I made one unit of ND only, and he was assigned to that.

So what's the deal? Why wouldn't he join one of the horse archer or YA units?