The problem (indicated) is that components on the (invisible) second row are placed behind the menu bar, and are therefor not visible. The two little yellow lines - which are pointed out by the arrows - are actually part of the top of the selection box.

To resolve this there should be a way to scroll through the components.

I am thinking more along the lines of a scroll bar to the right of the component bar and/or automatic scroll on parts selection, but a button to expand the area should work too. It might even be better, since it gives the player a better overview of all the parts.

The scrolling with the mouse wheel suffers from the same problem as the mouse wheel has in all the list: responsiveness. But SD is aware off that, so a fix may be coming (soon pretty please).

Thanks for reporting this, it has been noted.