I ran into a bit of a bug tonight, explained by the following screenshot:
So as the Duchess of Gascogne, I had married the second son of the King of Castille martilineally. At first it seemed to be a good choice. But then I got this event. Wait a second... we're talking about the same person here!
Within a couple years, the first son had suffered an unfortunate fall from a balcony, Prince Gundemar was heir, and Prince Gundemar had declared me a rival rather than a lover as the bug progressed. Soon, he inherited Castille, and not long after I declared war on Asturias to take a province. Asturias sent out a call for aid, and Gundemar decided that it would be a good idea to declare war on his wife. He had some success, too, as Castille's troops brought the tide of war back to a stalemate. Thankfully, the Pope was understanding of the strains that being at war put on a relationship, and was willing to grant a divorce. The war continued on for a few years, but eventually I gained the province I'd sought.
Having my liege as a prisoner also worked out. I managed to cajole a couple other dukes and duchesses to support Elective Succession in Aquitaine, the King acquiesced without a fight, and after that the King's first son married my niece matrilineally. Awhile later, I started a faction for Primogeniture in the realm. No one else supported it, and the King refused to allow it, starting a war. But since he was my prisoner, I had 100% warscore instantly and was able to force the matter. I have had to help put down a couple revolts to restore Elective Monarchy, but should have a dynasty member on the throne within a few decades.
Karling-supporting has paid off abroad, too, by successfully putting the former-regent-of-my-realm wife of one of my cousins on the throne of Lotharingia. She's happy, and the next generation of Lotharingian rulers will by of my dynasty.
The other main bug I've noticed is that the pictures of people keep becoming smaller and smaller circles. I haven't figured out exactly when it's happening, but I don't recall having that in my last game.
Edit: Just realized that Spain probably isn't supposed to be Visigothic in 867, either - it wasn't in 2.0.4. I was starting to wonder when it was ever going to adopt more Spanish culture, and found
this thread. It looks like Spain might be remaining Visigothic forever... oh well!