Multi-WAN OutBound NAT Not Work

[marcolum]

Hi Guys,
I've got a problem, I Have two WAN which route with 32ip each.
For InBound I used ARP Proxy to active those addresses with no problem.
But for out bound, I used NAT with BITMask. For the addresses for default gateway have no problem, But I can never use second WAN for outgoing, I found it always use default GW only. Follow with my settings:

WAN 1  202.XXX.XXX.212 GW 202.XXX.XXX.209  ->  103.XXX.XXX.128 / 27  (Default GW)
WAN 2  202.XXX.XXX.220 GW 202.XXX.XXX.217  ->  103.XXX.XXX.160 / 27

OutBound NAT Mapping:
WAN1  192.168.20.128/27  NAT 103.XXX.XXX.128/27  with Bitmask
WAN2  192.168.20.160/27  NAT 103.XXX.XXX.160/27  with Bitmask

When Use 192.168.20.128 for Outbound, It's used 103.XXX.XXX.128
but When  192.168.20.160 for Outbound, It's used 202.XXX.XXX.212

but If I set WAN 2 as default Gateway, It's just reverse.
192.168.20.128 -> 202.XXX.XXX.220
192.168.20.160 -> 103.XXX.XXX.160

So, I think something setting may miss or some bugs there which make the firewall  doesn't use the right Gateway.