Looking at the field names, I don't see any problem with the fields in your document either. It looks ok to me.
If I hook your merge document (labelsource.odt) up to a spreadsheet data source of mine (I created a query to match your field names), the merged output is correct.
I wonder if it's something off with your data source? There have been problems in the past with spreadsheet data sources not always being refreshed correctly. That was supposed to be fixed in 2.4.1 (as I recall), but maybe there are still some glitches.
You could try making a new database, but it would just be a shot in the dark.
Oops, wait a sec. When you open the merged output document, decline the offer to update the links. That's what's causing the duplicates.