This issue is part of
My csv-import file does not contain all columns that are declared in the Node Feeds importer.
When I feeds the file to the Feeds importer (updating a previously created/imported node), all fields that are not in the import file are cleared from the Node, except for the taxonomy terms, which stay intact.
Is this expected behaviour?
My use case is this: My node type is populated from 3 different sources. I did not combine the 3 files to 1 new file, but I created a Feeds importer with 10 fields. Now I feed the 3 files to the importer. Each file contains 7+2+1 fields.
An alternative would be to create 3 importers for the same node type, but this is not supported, until Attach multiple importers to one content type is committed.