That has happened to me too! When playing as the Julii on M/M, Iuvavum had rebelled from me back to the Dacians, with full-experience peasants and naked fanatics. That makes the peasants better in stats than hastati, with more numbers, and better morale too. Furthermore the upkeep is only 100...... That uber stack stalled my expansion in that direction by about five, six years, and even after I had taken Iuvavum, it was a ratty little hovel with barely 400 villagers in it. I recall being very annoyed by that.