Duplicate entry on empty webform file components

If you have a webform file component that is not required and the user submit the webform a Mysql Duplicate entry will appear.

Ex.

Duplicate entry '87-1274-17-0' for key 'PRIMARY' query: INSERT INTO webform_submitted_data (nid, sid, cid, no, data) VALUES (87, 1274, 17, '_old', '') 
Duplicate entry '87-1274-17-0' for key 'PRIMARY' query: INSERT INTO webform_submitted_data (nid, sid, cid, no, data) VALUES (87, 1274, 17, '_fid', '') 

That's because it tries to add _old & _fid to the no column that is numeric. Mysql converts them both into 0 and the duplicate entry error appears.

It works when a file is added but not when it's empty. But webform should not try to add _fid and _old to the database or am im wrong?