netlink support question for RFC 5549

Hi All, I notice that BGP can support RFC 5549 using configuration "ext_next_hop", bird can sync with kernel table using netlink assuming kernel support route with IPV4 DIP and IPV6 next hop. Sending route to kernel (nl_add_nexthop()) that don't check address family type that mean bird can send IPV4 NLRI with IPV6 next_hop to kernel if enabled "ext_next_hop". For bird receiving kernel route table, bird parse the gateway with nl_parse_attrs from rtm_attr_want4/rtm_attr_want6 based on address family , that mean if bird received IPV4 NLRI with IPV6 next hop, the gateway is parsed with IPV4 address since address family is IPV4 unicast on this case, does my understand correct ? If yes, this parse process have a bug ? Thanks Arvin