The thing i'm notocing is, and i don't know if it is intentional... But very rarely, when you click on a general in the field, he gains the 'spear carrier' retinue... The first time i didn't know what was going on, i clicked on a general and down the left side of the screen fell the 'retinue expands' trait... I opened it, saw that someone has gained spear carrier, then closed it as i didn't think anything of it... Then a little bit later i started to wonder how he gained the spear carrier retinue just by me clicking on him...

Then it happened again today... I left clicked on a general once half way through my turn, he was in northern Italy close to Mediolanium, and down the left side of the screen fell the 'retinue expands' notification... And the general i had just clicked on gained the 'spear carrier' retinue simply by me clicking on him...

Playing as Rome by the way... If it happens again i'll be sure to get a screenshot.