My vassal somehow created empire title.

[Unready]

I have conquered whole Iberian peninsula, created all kingdom tier titles, usurped and destroyed title of Emperor of Hispania and give all titles to my vassals as viceroys.
100 years after kingdoms of Andalusia moved to my de-jure Empire.
Rest of Iberian vice-kingdoms (Galicia, Asturias, Navarra, Castile) at that moment I gave to one vassal - duke of Leon.
With purpose for him to create kingdom of Leon (which can be created only by decision of owner of duchy of Leon).
With my additional monetary help sometime later he create the title.
And sometime later he create the title of Emperor of Hispania (still being my vassal before creation).
My character got strong claim on Empire of Hispania and I was too shocked so I immediately conquer it back.
I quite often do this trick to create Leon (and later revoke the title and use it as viceroyalty as all others).
But this was the first time as he can break the loose.

Strange situation and I was too shocked to get the savegame in-time.
[2.6.1.1]

PS Also I have found early savegame (I have published it at another bug report) - but in three test runs this situation didn't happened again.

 

[tviste]

I had something similar playing as the Roman Empire. The Viceroyal of Italy created the Empire of Italy and I had to reconquer the whole thing... at least it gave me a strong claim so I was able to do so in one war, but it really hurt my Threat level. (Not that I cared by that point)