In my Migrate module I have the path of the source file ( it's a CSV ) pointing to a file that exists on my server. That part works great. If I upload a file and rename it ( using the file browser module ) so that the uploaded file is the same name as the Migrate source file, I get some odd behavior.
The Migrate Import overview page doesn't complain that the file is missing, but the counts for the number of rows unimported are negative $x where $x is the number of rows imported ( from a previous run ). So if I had imported 60 rows before, uploaded, and renamed the file, refreshed the import page, I see unimported is now -60.