Thanks for your explaination. I understand, and it seems to be functioning OK with the following config. Is this the right way ? :

protocol rip rip1 {
#debug all;
interface "eth0" { mode multicast; ttl security tx only; };
honor neighbor;
authentication none;
import all;
export filter {                               # This block filters 192.168.1.0/24 out
                if net ~ [ 192.168.1.0/24+ ] then
                        reject "rip1:rejected:directly-connected";
                else
                        accept "rip1:accepted:not-directly-connected";
        };

}

protocol rip rip2 {
#debug all;
interface "eth1" { mode multicast; ttl security tx only; };
honor neighbor;
authentication none;
import all;
export filter {                               # This block filters 192.168.1.0/24 out
                if net ~ [ 192.168.5.0/24+ ] then
                        reject "rip2:rejected:directly-connected";
                else
                        accept "rip2:accepted:not-directly-connected";
        };

}

## eth0 is on the 192.168.1.0/24 and eth1 on the
## 192.168.5.0/24. The goal is to prevent an interface
## from advertising its own subnet