Double agent vs Assassin

Hello!
Such a question: my assassin meets with an enemy double agent. Assassin has the priority of battle 6, the agent is 5. Why does the agent kill the drills and change with the assassin in some places ?!
Such a question: my assassin meets with an enemy double agent. Assassin has the priority of battle 6, the agent is 5. Why does the agent kill the drills and change with the assassin in some places ?!