Play infantry showcase. (try a very easy difficulty as it would make it much easier to notice this, where you stand less of a risk of easily dying, and your team mates less of a chance to kill the AI before you get to witness this)
Try to play on the left of the valley, this is how I play it 80% of the time, this will get you closest to enemies almost barely detected, be sure to wait up for your slow ass team taking their sweet time to progress forward. Once close behind you, you should get close enough to see some AI exiting the villiage, towards your team, engage engage engage. (try not to kill it)
You might realize that AI will engage you, but once your team gets involved, the enemy AI will just blatantly ignore you. You could almost literraly run up to the enemy AI and punch it in the face =/
Also the AI at the back of the town, try chasing after them, ahead of your team, you might also witness them blatantly ignoring you as it did me.