I pursued this awhile back with no results, it is still a puzzling issue.  Any help what so ever would be appreciated.
 
When I park a call I get a notify message telling me the call park is confirmed.  Then at a random time, 2 seconds to 20 seconds out of the clear blue I get a message showing the call park is terminated.   The call is still active and can be picked up using the button on the phone.  The problem does not exist with extension blf.   using the console (fs_cli) at debug level 7 shows no activity at the time of the disconnect.

using version   FreeSWITCH Version 1.5.5b+git~20130721T031327Z~adf5e2f6ec (git adf5e2f 2013-07-21 03:13:27Z)
 
It seem to remember it worked correctly in the past but I am no longer sure.
 
Darcy Primrose
 
 
// this is for grandstream and yealink as well as snom parking.
<extension name="valet_park">
      <condition field="destination_number" expression="^(park\+\d)$">    
 <action application="answer"/>
 <action application="valet_park" data="my_lot@myhome.pbx2net.ca  $1"/>
      </condition>
    </extension>
 
// this is used to retrieve a call from park using snom.  I use snom 8.4.34, the load that works with blfs on freeswitch.
 <extension name="snom_valet_unpark">
     <condition field="${sip_to_params}" expression="proto=park"/>
  <condition field="destination_number" expression="^(\d{1})$">
  <action application="log" data="INFO 1 for Darcy unpark [${sip_to_params}]"/>
   <action application="answer"/>
   <action application="valet_park" data="my_lot@myhome.pbx2net.ca park+$1"/>
  </condition>
    </extension>
 
 
   <?xml version="1.0"?>
   <dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info" version="19" state="full" entity="sip:park+1@myhome.pbx2net.ca">
   <dialog id="park+1" direction="initiator">
   <state>confirmed</state>
   <local>
   <identity display="park">sip:1@myhome.pbx2net.ca;proto=park</identity>
   <target uri="sip:1@myhome.pbx2net.ca;proto=park">
   <param pname="+sip.rendering" pvalue="no"/>
   </target>
   </local>
   <remote>
   <identity display="park">sip:park+1</identity>
   <target uri="sip:park+park+1"/>
   </remote>
   </dialog>
   </dialog-info>
 
   <?xml version="1.0"?>
   <dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info" version="15" state="full" entity="sip:park+2@myhome.pbx2net.ca">
   <dialog id="2" direction="initiator">
   <state>terminated</state>
   </dialog>
   </dialog-info>