I normally have Box - Front, Box - Back and Box - Spine images in my Images tab of a game's Edit Metadata/Media, which allows the 3D Model Settings to render a 3D box using these 3 images.
Adding the Box - Full image results in the 3D Model Settings continuing to use the Box - Front, Box - Back and Box - Spine to create the 3D image, even that now the Enable Full Scan Images checkbox has been enabled.
However, If I delete the Box - Spine image then the 3D Model Settings will now use the Box - Full image to create the 3D box correctly.
By the way, The new Cassette option does not have an Enable Full Scan Images checkbox, so the 3D image created from a Box - Full image is incorrectly rendered here.