Fairy Tail Thread (Spoilers)

But they did, breaking the door in the present meant there wouldn't be a door in the future, thus preveting them all from time traveling and stopping the war. That's why I say it works weirdly. I do hope too they elaborate on it someday.

If you assume it changes the different timelines, you have an endless paradox with the door breaking/no-one coming to the past hence door didn't get broken. If it didn't change them, then it works out fine. It's more like Dragonball, future trunks coming back to the past and stopping goku dying didn't bring him back when he went back to his world, but it did stop the bad ending in the main timeline.