Confusion with Spymaster Scheming

[Lord_P]

The Scheme job on the Spymaster says that it can be used to coerce other vassals to join your factions. However, I have never got this to work. Sometimes the character promises to join and gets the small opinion penalty with me, but they do not join my faction.

What are the conditions for this to actually work?

 

[Fitzjacob]

Indeed, I've only been able to get them to leave factions correctly. I've got the promise to join, too, but they never do. Another half related issue is that players can rejoin factions without penalty after being told to leave them.