I've already tested this on three separate sites.
After adding an ftp destination, if the backup completes successfully, trying to visit the tab Saved Backups produces the following fatal error:
Fatal error: Call to a member function filepath() on a non-object in ../sites/all/modules/backup_migrate/includes/destinations.inc on line 886
After visiting the home page, another warning and an error appear:
Warning: fclose() expects parameter 1 to be resource, boolean given in drupal_ftp_ftp_to_file() (line 223 of .../public_html/sites/all/modules/backup_migrate/includes/destinations.ftp.inc).
FTP Error: Unable to download file: ./...mysql.zip.info from .
Deleting the .info file from the ftp server displays the Saved backup normally on the "Saved Backups" tab
Line 886 of the destinations.inc file is:
$info = drupal_parse_info_file($info_file->filepath());
Lines 220 to 223 of the destinations.ftp.inc file are:
// We have changed into the directory, let's attempt to get the file
$fp = @fopen($file, 'wb');
$get_file = @ftp_fget($ftp->__conn, $fp, $filename, FTP_BINARY);
fclose($fp);
I believe that @fopen returns FALSE and hence the error. I don't know what $file is supposed to be, but changing line 221 from
$fp = @fopen($file, 'wb');
to
$fp = @fopen($filename, 'wb');
seemed to be the trick. As this was done with very crude tests, I wouldn't suggest this as a solution.