Spell checking language is not respected on compile

I write in German, Scrivener is set to German of course and I selected “German” in spell checking options.
When I compile it to docx and open the file with my Office Program which has the best German orthography program included (Duden Korrektor), the text is always set to “English (USA)”.
Whatever I try, the language is always English and I need to change it manually for my German spell checker to work.

I am quite sure that this was working in one of the previous versions, Right now I use Scrivener Win Beta 2.9.9.20.