Whoa... that's quite counter-intuitive.
By not assigning a temporary file, one would assume that the worst case scenario would be for the file to not be created at all, and hence never touching what already existed.
But no.... it seems that it will actually delete even an existing file... perhaps because it assumes the final one to also be the temporary one in that case, and what it actually does is to delete the "temporary" one at the end?
Does it make a difference if you actually try to write some data to it? (probably not, which would probably prove my assumption here)