Update Import does not work

[Hap]

I have a large number of records that I'm trying to update using FM8 Advanced "Update matching records in found set" with the add new records option. The matching field is a unique ID number in both the existing database and the records to be imported. However when I finish importing, many of the records have been updated with data from different records in different fields. In other words record A, field 1 will be updated from imported record A, field 1, but field 2 will be updated from Record C. As far as I can tell , it is a completely random shuffle. Happens whether I import directly from another Filemaker database, Excel file and happens on both XP and OS X.

Comments/suggestions.