I think the same might have happened on my campaign, and it's on e/e.
All of the Brutii's cities were under siege, except for 2. I had my assassins destroy the barracks in both, yet they still somehow managed to recruit 2 legionary cohorts.

If anyone's interested, I have since destroyed the Brutii army (on the end of one turn, he sent 3 full stacks to attack my army, all were destroyed). I bribed the remenents of his forces and am now taking his cities. At present, I have about half, and all the others are under siege.