Rajesh,
VPN traffic will be processed o nthe Master first and then the cleartext will hit the backup. For a better understanding of what is going on, collect the debugs simultaneously on both Firewalls.
Most likely - the master in injectign he pak afte route lookup into the Trust network- as expected.
NAT-ing this traffic on the master and/or enabling 'mac-cache mgt' will get this working.