Creating port with fixed IPv6 address fails with: IPv6 address # cannot be directly assigned to a port on subnet # as the subnet is configured for automatic addresses

Issue

Creating an OpenStack port with a fixed IPv6 address fails with:
IPv6 address %(ip)s cannot be directly assigned to a port on subnet %(subnet_id)s as the subnet is configured for automatic addresses

(overcloud) [stack@undercloud ~]$ openstack port create --network=my-network --fixed-ip subnet=my-subnet,ip-address=2001:DB8::f816:3eff:fe17:77a3 my-port
BadRequestException: 400: Client Error for url: https://overcloud.mgmt:13696/v2.0/ports, {"NeutronError": {"message": "IPv6 address 2001:DB8::f816:3eff:fe17:77a3 cannot be directly assigned to a port on subnet cca33999-2b3a-4f91-8258-b8934ff297de as the subnet is configured for automatic addresses", "type": "AllocationOnAutoAddressSubnet", "detail": ""}}