Damn, that’s it.
I remember (a long time ago) looking at that option and not really understanding what it meant.
Not being a native English speaker, I even looked up the word, and that still didn’t drop a coin.
And then I probably did switch it on and off to see what it did.
And now I know…
I’m very sorry for wasting your time.
(maybe using some wording like ‘including sub-folders’ would be more obvious to simpletons like me 
)
Thanks @outsidecontext