I've seen this when importing data from excel files. Are you perhaps importing from Open Office's equivalent of Ms Excel?
The difference is in how the two applications store the data for a floating point number. Since they don't use the same number of signficant figures, you get this small difference after import. A single use of Replace Field contents with the Round Function on the found set of imported records can clean this up for you.
For More Information see: Import from Excel decimal errors
This is one of many acknowledged bugs that can be found in the Known Bug List thread here in the Report an Issue section of the forum.
It can also be downloaded as a database file from: http://www.4shared.com/file/8orL8apk/FMP_Bugs.html
Yes, equivalent Spreadsheet to Excel.
Thanks for info and advice. Looks as though it gives much grief to some people. Luckily it is an irritation rather than a major problem for me.