1) the service can only be as good as the underlying data. For Västra Götaland the boundary information is missing the service therefore returns the old ADM2 information. The alternative would be to not return anything.
2) For historical reasons the xml service elements were contained in a parent element, it is therefore possible to return a list of subdivisions. For the json service it is not possible to return a list without changing the result document and thus breaking existing applications.
3) The point is outside of the boundary and there are several algorithms trying to find something. With different parameters the result sometimes might be different. The alternative would again be to use only one algorithm and not return anything if nothing is found with the first approach.