Major Description
The Karaf main loads the config.properties (as a org.apache.felix.utils.properties.Properties) and load some additional properties in it (like System env/properties).
Especially, it writes one thing (and the only thing 
): the shutdown command.
It's the:
karaf.shutdown.command
property, containing an unique/random UUID to "secure" the Karaf shutdown.
If the property is not in etc/config.properties, Karaf will try to create one and write in etc/config.properties.
If the property is already there, it just uses it.
So, as a workaround, you can modify etc/config.properties to add:
karaf.shutdown.command=321DE18U23187
(or whatever you want).