Winning a Claim War for a Vassal

[Austregisel]

I won a claim war for a vassal of my vassal, he was an earl, so when I won the war he became King of Poland, but he did not continue as my vassal, it happened also when I gave a county to a guy who had a claim in france, I pressed his claim and won the war, turning him into a king, but he was independent, what am I doing wrong?

 

[EmoPro]

Its mentioned before you push the claim, whether you would keep him as a vassal or not after pressing said claim.
IIRC to have him remain as your vassal you need EITHER:
- said claim is in your dejure territory
- the claimant is of your dynasty

In essence it removes the vanilla method of granting a kingdom claimant a barony and press said claim to add the whole kingdom into your HRE