Here’s a video depicting the issue:
There are a bunch of properties that ARE set on the default locale, however, when I change to another locale, the properties aren’t set anymore.
How do I set this property once for all locales?
Note that, “reset to primary locale” doesn’t do anything…it’s not even clickable.
Can it be, that you have to reset the whole component ? (drastic, I know)
I had a case in my project, that when I added a property to a existing component, the new property wouldn’t show for the other locals. When I reset the component’s localizations, the property appeard.
Tried that. 
I finally just bailed on it and re-did the entire section without any properties.