Strange...
I play H/M as Romanus and the Charthaginians behave as they should. Maybe it's the way you play which triggers or not.
From 264 till 240bc I had the Punic war near Messana going on with their armies and fleets annoying my force.

I just ended the first Punic by Force Diplomacy ceasefire and the handing over of Lilibeo.

No complaining concerning the ai's behaviour sofar...

Seems balanced enough on Hard strat map