That is very peculiar,
When I looked at the settings, these comboboxes have a maxdropdownitems set to 8, for some reason this is being ignored on my setup
On my maching, the movie actor drop list displays about 30 movies before the scrollbar is added,
I have 15 sets which are all shown without the scrollbar,
Both the max genre and max actor comboboxes display all their options without scrolling.
I've increased the values for the next build.