I've just recorded 3 fuel up's, but instead of calculating the mpg between each fill up, it's done it from the first fill up to the third (the complete total of miles I have done).
If you take a look at your View All Fuel-ups page, it looks like you have some fuel-ups out of order. Your odometer reading on Aug 30 was 21,035--but your previous entry on Aug 25 is higher at 22,798.