So you did a drag-n-drop from the calibre library folder to the available formats window in the edit metadata area. This is essentially a "move" and after a file is successfully copied/moved to the new location (same location in your example) the original would be deleted. This causes a 0.0 byte file.
You can't do this via two different file managers in Windows because it recognizes they are the same and throws up a error box and an annoying sound to let you know this isn't right.
It seems calibre (python) isn't so forgiving. I tried this myself and did end up with a 0.0 byte file that was garbage.
Read here to find out how to create a ticket. But like the old joke, Patient: Doctor, Doctor it hurts when I do this.... Doctor: Well don't do that.
Congrats on being unique enough to find this "Opening of destruction".