ARM 2019.1 VPN / AC3200 Wireless Ethernet Bridge mode does not work (as a client)

Trying to set up the RT-AC3200 interface as a Wireless Ethernet Bridge fails. The radio link is seen at the host but nothing else happens. Looking at the Ethernet packets at the host end it seems the client is sending a garbage ARP request to get the MAC of the default gateway and is stuck in a loop sending more bad requests.