Rsync not working with restricting security options in 6.4.1

After updating to Readynas OS 6.41 my rsync backups over SSH with KEY to another server do no longer work. 

The remote server has this option in /root/.ssh/authorized_keys

command="/usr/local/bin/rrsync /mnt/disk/",no-pty,no-agent-forwarding,no-port-forwarding,no-user-rc,no-X11-forwarding ssh-rsa READYNAS PUCLIC KEYHERE

The readynas did to backups to this system without problems... until i moved to 4.6.1 (from 6.2.5). 

It works if I: 

A) Either put this in /root/.ssh/authorized_keys on the remote server:

    command="/usr/local/bin/rrsync /mnt/disk/" ssh-rsa READYNAS PUCLIC KEYHERE

B) Or if I issues this command from the CLI on the readynas (ssh login to NAS): 

    rsync -avlz -e "ssh -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null" --stats --progress --exclude 'home_dieter/snapshot' /data/home_personx 10.0.0.xx:/

My conclusion: the 6.4.1 does add some command to the Rsync over SSH that failes to work with a security restricted Rsync server. 

It's NOT that the Rsync does not work together in terms of incompatible Rsync protocol versions, as far as I can tell. 

Can someone perhaps tell me what Rsync options the 6.4.1 uses with Rsync over SSH? What has changed with 6.4.1 compared to 6.2.5? 

info: My NAS: readynas 102, backup server: Debian “jessie”