There is a problem when editing old fill ups - if you make an error in entering the price per gallon, it will warn you when you try and update, but at the same time it will change the date to today's date, so when you fix the price and update, the wrong date (today's) is used for the old fill up.
Originally I had entered my price per gallon without the 9/10s, so I went back in an edited my fill ups changing the price. I mis-typed the amount and when I hit updated it warning me with red message saying the price was too large, when I fixed the price and updated, it had changed the date to today's date, instead of the original fill up date. The result was confusing, and I did not know what had gone wrong at first. I deleted the fill up and re-entered to fix the problem.
I was reviewing the edit page myself, it shows the date field at the bottom, did you try to set the date to the correct one then submit the changes and it still had the wrong date? If not, try that first.
One other way I think one way to fix this problem, is to go in, delete the entry. Make a new fuel up entry and set the date (there is a place for the date in there too) and then re submit it, if this is a bug with the edit tool.