I am not the expert on this matter, but I know a thing or two.

Airlines sell tickets in advance (way in advance) and in bulks, so a change in the oil price must be for a long period before airlines can act accordingly and change the fuel surcharge, if airlines acted quickly and changed the price according to the current low price and then a few weeks later oil prices go up again, then airlines are screwed because they would have sold many cheap tickets in the future where the price will be higher and the _extra_ profit they made due to the low prices in the current period will not cover the losses in the future.

Another thing, it is a quick unanticipated extra profit for the airlines, and who doesn't like that. 

Regarding the price buffering, most (if not all) airlines made their fuel surcharge according to the highest possible fuel price they faced, and it is too dangerous for them to change it as I said earlier unless the prices are low for a long period.