s3cmd fails with --encrypt option when piping

[Cosmicoppai]

root@14778e0764d3:/usr/local/bin# dd if=/dev/urandom bs=1M count=10 | s3cmd --encrypt put - s3://pl-backups/test_file
upload: '/tmp/tmpfile-AxsIy1LTkehTIoLex3yR' -> 's3://pl-backups/test_file'  [1 of 1]
 70 of 70   100% in    0s     2.63 KB/s  done

root@14778e0764d3:/usr/local/bin# dd if=/dev/urandom bs=1M count=10 | s3cmd put - s3://pl-backups/test_file_no_encrypt
10+0 records in
10+0 records out
10485760 bytes (10 MB, 10 MiB) copied, 0.193257 s, 54.3 MB/s
upload: '<stdin>' -> 's3://pl-backups/test_file_no_encrypt'  [part 1 of -, 10MB] [1 of 1]
 10485760 of 10485760   100% in    0s    64.09 MB/s  done