Lighting 'Preview Mesh' not displaying correctly on \

I had to Google quite a bit to even find out what this thing is called, but mine isn’t displaying correctly in some levels. I suspect it’s nav related, but not too sure at this stage.

In some maps it’s being drawn with its pivot at the camera position (wherever I move) and so surrounding the camera, rather than at the cursor in my scene. This makes it pretty useless because I can’t see the colour swatches, just the backs of them, and I can only just see the bottoms of the spheres by looking up. Any ideas?