PJSIP Trunk configuration reverting back to "Conf. Mode = Simple" on save

When the Trunk configuration page for a PJSIP trunk is loaded, the value of the field "Configuration Mode" is always equal to "Simple", even if the trunk is setup and saved with "Configuration Mode = Advanced".

If someone after correctly setting up a trunk with Advanced mode goes back to the Trunk page to change whatever parameter, if the user is not careful to change the field "Configuration Mode" to Advanced, on saving the changes the configuration will revert to Simple mode and as a result the trunk will go down.