Hi TK,
The post here:Close ports 32015/500 for PCI compliance is also in regard to this particular issue and deployment.
As an example:
A Balance 380 has 3 WAN connections
L2TP connections are required, but we only want to open up the required ports on WAN 2 leaving the ports closed on WAN1 and WAN 3. Right now, by allowing L2TP connections, the required ports remain open on all WAN connections regardless of whether or not the WAN connections are selected to allow L2TP connections in the configuration. I hope this helps explain things.
-Topher