Reserve team in non playable league, issue with 'make available for reserves'

[DavyDepuydt1]

I'm managing a team in french League 1, my reserve team plays in National 2, which I have not chosen to be playable.
Players in my reserve team get generated appearances for matches they play in National 2 and have match fitness accordingly.

However my strategy with my first team is to make those that don't play much "'available for the next reserve game" from time to time.
But in this situation this does not seem to work, it seems that they don't get any games and gain match fitness unless for real playable games (friendlies).

Is this a bug? or a chosen design limitation? I was hoping that they would get these fake generated appearances and gain match fitness just like those who actually are in the reserve squad.