... and trade confirmation (open trade, go to the different instance, confirm trade)

L2_GameServer/java/net/sf/l2j/gameserver/network/clientpackets/TradeDone.java

@@ -78,6 +78,14 @@ public final class TradeDone extends L2GameClientPacket
 	            player.sendMessage("Transactions are disable for your Access Level");
 	            return;
 	        }
+
+	        if (player.getInstanceId() != trade.getPartner().getInstanceId()
+	        		&& player.getInstanceId() != -1)
+	        {
+	            player.cancelActiveTrade();
+	            return;
+	        }
+
 	        trade.confirm();
 		}
 		else player.cancelActiveTrade();