Epirotes never aid Arverni in battle

During my second playthrough as the arverni, I get the mission to help epirus by attacking vindobona and Ak-Ink again, and I noticed something.

Through both my first and second playthrough, the Epirote general will stand next to the town, and not help during the attack. I tried multiple times, I even broke my alliance, and remade it using force diplomacy, gave them military access, gave myself military access, and nothing.

And the first playthrough, on a different install (on a different OS, Ubuntu w/ Wine vs Windows 7, no less) they didn't help either. What gives?

I've even waited until the last city attacked me (I am actually playing it right now on my desktop) and still, the epirotes didn't show up during the pre-battle screen.

It's happened in both 1.1 and 1.2.

Am I doing something wrong?

I doubt it: the Epeirote-Gaul alliance is just a script that affects diplomacy and spawns an army but nothing else. For the purposes of the game engine, you are fighting a normal siege battle. Maybe the option that limits reinforcement during battles also affect allied armies?

The enemy usually gets reinforcements. Also, if there are too many units, usually what happens is I get the enemy delayed event, and if the enemy's army on the battle field doesn't all route at once, they show up later.

I might test it and see if I can get reinforcements in battle, I know the enemy gets them