1. Have one unit attack a group of IDLE villagers. The one under attack will fight or run, but the others will just stand around waiting to be attacked. When the villagers are NOT IDLE, they do not run, but continue working. (All this does not apply if the town bell has been rung, but the AI evidently does not do that very often, or perhaps I have noticed this behavior only when the villagers are out of range of a town center's bell.)
2. Put an army of non-ranged units into aggressive stance, and then move them across the map until the front unit can see an enemy. He will attack, but most (or all of the others will not). It seems that only when an enemy appears in a units line of sight will he attack. What should happen is that if any unit attacks, all other units who can see the unit attacking should move up to that unit's position, and attack if an enemy is now in their line of sight. This would be more realistic.