MS excel making unwanted auto-copies

This happens on 1 user using a network drive.

She opens a excel file and does some editing, saves and closes.

Result is that there’s the .xls -files ok, but also a copy with a name that hasn’t got the .xls -extension and contains just some letters and numbers.

The autobackup-setting makes file names beginning with ~, so these ain’t those. Or could they be somehow related to it?

Is it something else?