When you initially import a raster as an image object into SketchUp and place it on a surface, SketchUp automatically adds the “glue” property to the image. One of the characteristics of the “glue” property is that the image take visual precedence over the surface even though they share the same plane.
Unfortunately, the copy past method does not initiate the addition of “glue” property.
A) Import the raster image again.
B) Copy and paste the image on the second surface, explode the image while on the surface. The image is now a texture mapped onto a surface. While the textured surface is selected, make it a GROUP. Because you are creating a GROUP comprised of a surface sharing the same plane as a surrounding surface, the new Group will get the “Glue” property. You can then position the new graphic as needed in the secondary plane.