The "release of region into a vassalized buffer state" feature from 1212 mod - why the button disappears??

[moralrelativism]

I remember when playing the 1212 mod a few months ago the game definitely had such a feature (which was amazing).
The description on its steam page confirms that:
"Buffer States: Release vassal buffer states from conquered territories where your direct control may be tenuous."
There ought to be a "creating vassal state" button shown up underneath the Province Effects bar upon clicking a region, as seen here:
https://i.imgur.com/lVsggLp.png

However, now the button is no longer there. I tested it with a clean 1212 mod (i.e. game run with only the standard 1212 mod files and nothing else). Simply can't make the button show up.
Has the this feature already been suspended or is it a case of my game having corrupted files?
Some advice please! Thanks!

[alhoon]

That feature in the steam page is the reason I installed this mod. I hope it was not abandoned.