[Freeswitch-users] call park blf

I use park+{slot} to park calls using keys on snom and grandstream phones. The busy lamp field lights but goes out shortly after, about 5 seconds. However, the call is still on hold and can be picked up by pressing the illuminated light. When I do a sip trace, there is a notify message saying the park+{slot} has been terminated. Any ideals. Incidentally, all other BLF's work prefectly. Following is the settings in the dial plan