I would check that in <file><properties> that it says it was saved when you
last saved it.
I would also check that it is not been converted to a template format and is
opening a copy, not the document itself.

If neither of these indicate a problem. I would use save-as for awhile. If
this is the only document you have that is doing this, It may be worthwhile
copying everything to a new workbook. There may be some corrupted code in
the current file.
"Ming" wrote:

> I have a spreadsheet where some cells reverted automatically to it previous
> values. This is the first time that I have anything close to 130 columns and
> 8000 rows.
>
> I would change some values, save and make some more changes. Then all of a
> sudden when I noticed previously changed data were the same as the original.
> I thought I was going insane, but it did happen more than one occasion.
>
> I did worked on the worksheet in both Excel 97 and Excel 2002 before. Any
> problems there?
>
> Ming