Already locked it once.

src/main/java/com/gmail/nossr50/party/PartyManager.java

@@ -267,7 +267,6 @@ public final class PartyManager {
 
             if (password != null) {
                 party.setPassword(password);
-                party.setLocked(true);
                 player.sendMessage(LocaleLoader.getString("Party.Password.Set", password));
             }