I've only just noticed this tonight so don't know whether it's unique to 1.6, BI Enhancement or if it's always been there. As Romano-Brits I had two shady characters who plied their trade as assassins in Vicus Saxones. They rapidly reached 10 eyeballs apiece and were soon killing for fun. After a while it was apparent that the Franks had a seemingly endless supply of family members, having lost around a dozen to my assassins.

Apparently, when a family member was bumped off he was immediately replaced by, for example Captain Faramund. At the beginning of the next turn, Faramund had become a family member with one or two stars. Repeat ad nauseam.

Prolific, fertile Franks, Men of the Hour or another bug in the AI's favour?