I've seen the biggest inconsistency and game breaking bugs regarding that agreement. As Poland I had the allies on my side and went to war with Germany. Germany at that time was at with the Russians. But suddenly the Germans called in the Russians to attack me even though they are at war..? Also switching factions mid war can end up with a game over screen at times as you instantly capitulate upon changing factions.. it's just odd. You should make it impossible to invite a person to a faction while at war