Trying to restrict access of a specific port to a specific IP address.  Set up these rules:

ID   Name              Source        Destination    Source    Destination   Policy   Service Type     Direction    Effective Time
                                                    Network   Network 
2    VoIP_Admin        VoIP_Vendor   PBX            ---       ---           Allow    PBX_Admin        WAN IN      Any
3    Block_VoIP_Admin  !VoIP_Vendor  PBX            ---       ---           Block    PBX_Admin        WAN IN      Any

It worked for a few days then suddenly it just stops working.  The port became open to all!

I changed the rule #3 to 'Allow' then back to 'Block'.  It works again!!