Having this same issue. In Sweden, for example, all books are taxed at 6 % instead of normal VAT 25 %. Local regulations state that shipping VAT should either follow the main VAT of the order (i.e. the VAT category with the largest sale value on the order) or be split out based on actual amounts for each VAT category.
But currently, when I try to order only a book, it sets the VAT for the book to 6 % due to my override, and then 25 % for the shipping. Even though there are no items in the basket that have VAT 25 %.
There is even a section on this in the Help Center, but no information on how to activate it.
