The ftp_upload.php has not been touched since Dec 2, 2010.. so I don't think anything changed with regards to the transfer of files.
Check your ftp server logs for more clues... or paste us the errors DA returns if the upload fails.
There are no rollbacks, but if there are any issues, we'll simply fix and re-release.
If anyone else is having similar backup issues with ftp, please let us know.
John