I had a very similar situation too when I played as either of the Gallic factions with BI. Carthage just kept sending full stack naval invasions practically every turn to take Tolosa once I had secured it (but not earlier). Though would even walk through the whole of Italy, while at war with the SPQR, only to attack me, their ally, at Tolosa.

Nothing like that has ever happened to me in the RTW or ALX exes, though.