I was trying to make a detailed view in a layout earlier, so I made a circle and converted it into viewport. However, when I placed the circular viewport over the main viewport (which contained a raster image), I could only see what was in the circular viewport when it wasn't over the raster image part of the main viewport. I tried changing the draw order of the view ports, but nothing seemed to work. I eventually just got around the situation by creating the detailed view in model space, but I'd still like to know if doing this via. viewports is possible.
 
Any ideas?