If we set icons for the accordion element in the theme style, these icons have no immediate effect when we insert a new accordion element in our page. Instead, the arrow icons that are pre-set on the element level are applied. Only when we delete these pre-set arrows, then the icons defined in the theme style are applied.
IMHO this makes no sense. Theme styles are meant to define the default styling for an element, and these settings should therefore be applied when inserting a new element of that type.