After altering the Hide-NAT-Relation there was no difference in behaviour as I would have expected. I tried pinging external IP-Addresses and DNS-Names with no successful response and 100% loss.
Yes, I tied saving the configuration and executed a rule updatejust to make sure.
Nothing changed this behaviour.
I then deleted the Hide-NAT-Relation. I executed a rule update and then reconfigured the same Hide-NAT-Relation as I had altered the original one to.
Now it works. :P
It seems, that even though it is possible to edit/alter an existing Hide-NAT-Relation, it just does not work. :roll: