While I am not certain why this happens in a detail, I do know of a way to get what you want to work. I have always dragged a copy of the generated 2D information to a set distance to the right, and edited that for my working drawing. That copy will let you apply the graphic override to it. You still get the same pop up but you don't have to rebuild the detail. Another advantage to using the copy of the generated detail is that if you have to rebuild the detail, any dimensions or labels associated with the copy remain. If you use the the 2D data it originally gives you, all those elements loose that association when you rebuild.
Margaret Cochran - BIM Manager,Technical Designer
ARCHICAD 7-23
HP ZBook 17, Windows 10