Ipv6 + multi-wan + gateway group + NPt + inbound problem

[kingwilliam]

pls accept my poor english.

problem:
I have 2 wan & 2 lan on pfsense
1 lan for ipv4
1 lan for ipv6
2 wan formed gateway group for outbound & inbound.
and have 2 gateway group, 1 for ipv4 and 1 for ipv6.
and i have web, ftp and mail server at lan with ipv4 & ipv6.

ipv4 inbound and outbound work perfectly.
ipv6 gateway group outbound same work perfectly.
but ipv6 inbound have tricky problem, only ipv6 default gateway set on system->routing->gateways can function, and beside gateway can't accces from internet.
if i set default gateway at wan1 ipv6, only wan1 ipv6 can access from internet, wan2 network can't accces from internet.
if i set default gateway at wan2 ipv6, only wan2 ipv6 can access from internet, wan1 network can't accces from internet.
if both wan ipv6 remove default gateway, only latest default gateway still work.

may i know this is normal ? or a bug?
may i set ipv6 multi wan inbond same function with ipv4 inbound?

scenario:
pfsense version : 2.1.1

wan1 : 2001:470:1:1:: (HE.net tunnel)
wan2 : 2001:470:2:2:: (HE.net tunnel)
lan_v6 : fd03:3:3:3::
lan_v4 : 192.168.0.x

system -> routing -> groups
created group name : NLB_ipv6, both wan Tier are 1.
created group name : NLB_ipv4, both wan Tier are 1.

firewall->rules->lan_v6
create
interface : lan_v6_ipv6
tcpip : ipv6
protocol : any
source : lan_v6_ipv6 net
destination : any
Advanced features -> gateway -> NLB_ipv6

firewall->rules->wan1_ipv6
create
interface : wan1_pv6
tcpip : ipv6
protocol : any
source : any
destination : lan_v6_ipv6 net

firewall->rules->wan2_ipv6
create
interface : wan2_pv6
tcpip : ipv6
protocol : any
source : any
destination : lan_v6_ipv6 net

firewall->NAT->NPt
create
interfnace  : wan1
internal    : fd03:3:3:3:: / 64
destination : 2001:470:1:1:: / 64

interfnace  : wan2
internal    : fd03:3:3:3:: / 64
destination : 2001:470:2:2:: / 64