I am sorry for the inconvenient, but when I had the idea to enable the MASQUERADE for the packets to be forwarded to a real server, I did it because I wanted the port forwarding also works fine when the clients are in the same IP subnet of the real servers. Now I understand this is not a good idea and I am going to remove this automatic setting in the next release.
At moment you could add the following line in the file /etc/rc.local:
iptables -t nat -D POSTROUTING -j SNATVS
and then reboot the router.