L2 Bridge sets packet attribute to mark the packets being bridged already and will drop the received packets with such attribute set.
VDL2 ARP suppression will restore the VDR packet attributes in the cases where its ARP table is empty. Once its ARP table is populated either through controller query or local resolution, subsequent ARP request from VDR bridge will not have the VDR attributes restored.
Since VDL2 does ARP suppression by looking up from its ARP table, the source port will be that of the VDR's uplink. So VDR bridge sees this MAC from uplink but also in its FDB pointing to local port, so it will drop the frame assuming underlay U-turned the frame.