Seems that it allows others to take the quest. When one person is already on it and another enters the pillars reset, as a result one of them cannot complete the quest. Rather bothersome!
It is rather confusing, as it messes up both depending on where they are in the quest. If the first one is just finishing and gets through the door, they get the item still, however the second guy doesn't, but they get the exp. Its very very strange when this happens.