Attribute "locked" not allowed in <property> for non-system files

I would like to configure a locked property (kiosk mode) in my local configuration for the purpose of keeping my configuration declarative. Example:

<?xml version="1.1" encoding="UTF-8"?>

<channel name="thunar" version="1.0">
    <property name="misc-single-click" type="bool" value="true" unlocked="nobody"/>
</channel>

This is currently not allowed, xfconfd will log this error upon starting Thunar (in this example):

Error parsing xfconf config file "/home/lordmzte/.config/xfce4/xfconf/xfce-perchannel-xml/thunar.xml": Attribute "locked" not allowed in <property> for non-system files

Of course, this is intended behavior, but I do not see why. Are there any security concerns with allowing locked properties in local configuration?