It must be part of the revised AI.

I'm playing a Julii campaign VH/H. After taking Segesta the Senate requested the I take Caralis. To keep the north secure I accepted a trade agreement with Gaul. In 268BC the Scipii allied with Gaul. After I took Caralis and completed the Senate requested blockade of Carthage the Senate asked me to take Patavium. At that time both the Julii and the Scipii were at war with Carthage. The Scipii took Lilybaeum. I laid siege to Patavium and the Scipii declared "our alliance in tatters". The next turn the Brutii declared their alliance with the Scipii in tatters. The SPQR and the Brutii declared war on Gaul in sympathy with us (Julii). The Scipii must have broken their alliance with the Gauls at that point but I don't recall seeing a message.

So now the Julii are allied with the Senate and the Brutii and the only ally the Scipii have is the Senate. The Scipii and the Brutii both have armies staring at each other across their common border.

Oddly enough after all this the standing trade agreements were still in force so Patavium is trading with Messana.