Hey there,
after testing the behavior a bit, there are probably two bugs I noticed.
One "bug" is resolved with an ifreload or with ifup -a.
1. A ovs_bonds Interface have the mtu of 1500 - despite setting it to 9000 (ovs_mtu 9000).
netstat -i (only bond0 and vmbr9)
Kernel Interface table
Iface...