It's always happened. Annoying and discouraging. Getting killed by your own guild/nation in a PK war just makes you wanna sit on the sideline and watch or log-out.
In my opinion, GMs should add 2 new commands to the game:
/party nation (makes you unable to give damage to people from your nation)
/party guild (makes you unable to give damage to people from your guild)
*I voted for BOTH*