My thermos bottle's instructions say:
Füllen Sie keine kohlensäurehaltigen Flüssigkeiten oder Trockeneis in das Produkt. Füllen Sie keine alkoholischen oder öligen Flüssigkeiten in das Produkt.
This translates to:
Do not fill carbonated liquids or dry ice into the product. Do not fill alcoholic or oily liquids into the product.
I suppose the reason you're not supposed to fill carbonated liquids or dry ice into the thermos bottle is that the bottle isn't able to handle the pressure which builds up if you close the lid. In the case of dry ice, it might also not be able to cope with the temperature of it. I further suppose that oil can wear down the seal.
But why are you not supposed to store alcohol in it? Sure, some alcoholic beverages are carbonated, but those already are excluded. What about beverages like mulled wine?