The "potential successor" became faction leader instead of heir

[Paltmull]

In my Aedui campaign, the general that I had chosen as potential successor became the faction leader directly when the old faction leader died. The original faction heir did not become leader, but remained as heir. IIRC, this did not happen in my Pergamon campaign so maybe it's the Teutonic family system that is causing trouble?

On the other hand, maybe this shows that there's a way to choose the next faction leader rather than the heir; so it might not just be a problem but an opportunity as well...

Has anyone else had this happen?

EDIT: See the attached pics below: Tankogeistla remained heir after Kokolitanos died, and Dennoros became leader.