Papajack: Your July 4 fillup is marked as a partial fill. When there's a partial fill, no immediate calculation is done for that fill, or the next. This data is still used in your overall lifetime vehicle average though. If this is an error, edit the fillup again, and uncheck partial fillup, and you will receive calculations for the past 2 tanks.
Your previous entry only has an odometer reading. The database is probably treating this as a partial fill. I don't think the programmers have maintenence entries implemented in the database yet. This is something that is scheduled for future release. I would edit your last fillup, and in the notes section put the date and mileage of the oil change, and delete the oil change entry. Then it should calculate as normal.