I have the same issue with the parking BLF and RESTAPPS using yealink 46G and the most recent version of FreePBX 6.12.65-31. All modules are up to date. Once a call is parked the light will stay lit. This seems to only be an issue when using asterisk 13. I also get a notification that Parking is Enabled on the screen?. Asterisk 11 works fine with the RESTAPPS parking BLF. There seem to be multiple bug reports related to this:
http://issues.freepbx.org/browse/FREEPBX-10581