I've expirienced this once, and ironically it happened after one of my teammates shouted not capture the enemies right side portal or it would critical game state. Since I had never seen it before, I did anyways, and it actually did happen.
My hypothesis then, since this had never happened before or since, is that certain players create this issue for whatever reason while others only ever expirience it when they play with those players. I can't perfectly recreate what happened, but I've been in games since where every flag on the map was owned by my team, and games where every flag was owned by the enemy, and it didn't critical game state. Thus, if it is related to flag capture, it's limited to certain computer setups or very special in game circumstances.
