Ok, I finally managed to solve this annoying issue. The problem was related to the use of Categories - like All movies, Unwatched movies and so on. For each Category it's possible to select a default view - and all default to List View. So to cut a long story short - if Organize movies by category is enabled in GUI Settings the option By default show movies in ... has no effect - it is being overwritten by the categories setting unless the category setting is set to Use Parent View. In this case the GUI Setting is enforced.