Found it during manual testing of JENKINS-28881

Analysis results:

• AbstractFolder#properties is a persisted list
• Persisted list is being automatically saved on modification
• Persisted list requires the correct specification of owner to be saved. Owner info is not persisted on its own
• When the plugin loads properties from the disk, it does not assign properties owner if the list exists
• Persisted list uses the default owner (Saveable.NOOP)
• When Persisted list is being saved by AbstractFolder#addProperty(), the plugin actually saves NOOP instead of folder

The original code:

if (properties == null) {
            properties = new DescribableList<AbstractFolderProperty<?>,AbstractFolderPropertyDescriptor>(this);
        } 
        for (AbstractFolderProperty p : properties) {
            p.setOwner(this);
        }
...