Package: ftp.debian.org Severity: important Transfers between the upload queues and ftp-master / security-master are done using rsync. The connection sometimes fail, which causes some files to be missing and the package to be rejected. In that cases it's not possible to reupload the package from the buildd as the signature has already been seen by dak.
I guess the same strategy than in dput / dupload should be applied, that is to transfer the changes file last. That way the next rsync run could transfer the missing files.