I should note, someone suggested that the fare allocation might result from a hold on a ticket while someone books it. I can tell you Delta does not do this. I was in the middle of booking (I had picked outbound and return flight and then when it loaded the summary page it told me they could not book my ticket and made me start over at a higher price). I reached out to Delta and they said it wouldn't even hold it for any amount of time if I were already on the summary page, but rather the price can change at any moment up until the point you have a confirmation number.