This is a dialplan approach to fix the feature key sync loop/race with yealink phones. This aproach may also need to be extended to the Call Forward dialplans as well. It limits the number of simultaneous calls for a particular user to change their DND/Forwarding status to a single call at a time. This prevents the infinite loops that the yealinks can get into if the user presses the DND button too quickly with feature key sync enabled.
I am also reverting the lua fix because it was not reliable and can still easily allow the loop to occur.
FusionPBX
demonspork