-1.  This changes the documented behavior of a commonly used function.

FWIW:  MoveFileEx() with MOVEFILE_COPY_ALLOWED isn't transactionally isolated.  Other processes can see the new file being created, and watch its size increase, while the old one still exists.  It isn't atomic, either: in certain error cases, e.g. if the process's permission to write the target file is suddenly revoked, it will fail after making changes to the filesystem.

Also-- it looks like the test leaves one of the temp files lying around!