Swedish culture taking over France

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I was playing my game (v. 1.03b) in 1210 as the Duke of Anjou when a message pops up and says that the county of Maine had "converted to the right faith" - I think it had gone Heretic, though I myself hadn't noticed it and I do check on my demesne often - and that it had "changed its culture to swedish".

WTF?

why did it changed culture? And why to a completely alien one? [my ruler is frankish catholic].

I then clicked on other french provinces, and noticed that the county of Carcassonne (my vassal) was also of Swedish culture, while the county of Cadiz in Spain (owned by the King of France) ALSO now had swedish culture... :wacko:

In addition, I noticed that the county of Saintonge (which had reverted to the germanic family of Frankonia in the XIth century), now had Danish culture...

Is this WAD? What's happening?

 

[unmerged(21937)]

Iirc the Conversion event that changes culture too can happen with same religion, to simulate cultural changing. Also as it changes to realm-culture, it checks that from the highest ranking guy in the realm. So if king of France is swedish, all conversions in France that change culture result in swedish provinces.