I always went with the "clear cache" theory until a couple of weeks ago I was looking at a one way JB fare on my laptop...decent price so I went to my desktop so i could print the receipt and the price was $70 more each...

I then turned my laptop back on and the original price ($70 cheaper) was there...booked it.

No explanation for that one....different compters and not logged in tomthe JB site on either