I had almost finished a design (small 2-layer board) and was doing final checking and creating GND plane on the bottom layer. The GND tracks on the top layer are now invisible. They seem to still be present in the design, just not visible on the top layer. If I create a track on the top layer (or bottom layer) then it is visible until I rename it GND. Then it becomes invisible. If I rename it something else it becomes visible again. Fortunately I saved a copy shortly before and it appears OK. I attach two screen shots of the same board area. How can I get the GND tracks visible again?