virtual server on a different routing group

I'd like to use a different routing group to provide balanced web services on an internal VLAN that must not be routable from the normal Internet traffic. I'm Using BigIP 11.2.1

I'm not able to forward traffic to the backend servers.

Here are my two test virtuals:

ltm virtual VSVR_TESTROUTING {
    destination 192.168.200.102%1:http
    ip-protocol tcp
    mask 255.255.255.255
    pool pool_courtesy_page
    profiles {
        http { }
        tcp { }
    }
    snat automap
    vlans-disabled
}
ltm virtual VSVR_TESTROUTING2 {
    destination 192.168.100.203:http
    ip-protocol tcp
    mask 255.255.255.255
    pool pool_courtesy_page
    profiles {
        http { }
        tcp { }
    }
    snat automap
    vlans-disabled
}

The pool is correctly routed from routing group 0 (default) where it resides. Trying to access http://192.168.100.203/ works fine, while any access to http://192.168.200.202/ is reset just like when the pool members are not accessible.

Of course the routing is OK, and if I attach to VSVR_TESTROUTING an iRule containing just a HTTP::respond 200 content {....}, the virtual correctly returns the given content.

I did a tcpdump on both VLANs, there is no traffic at all related to failed accesses to VSVR_TESTROUTING, while succeeding accesses to VSVR_TESTROUTING2 are visible (SNAT-ed with the right self-ip)

It really seems to refuse to forward the requests to the pool, and not simply forwarding the request to the wrong default gateway, but I don't understand why...

Does this scenario ring a bell in anyone's ear?

Thanks, Angelo.