Ok people before you all go blaming inventor on this one I think i know what the problem is. If you all look at the picture more closely you'll see that the xy, yz, and xz planes are highlited in a special way. What you are see are those planes. There is probably some setting that you changed to where those planes are always visible. I would ask autodesk about that before you go searching for some type of bug. This is just me talking though. Actually now that I look at it closer I think that there might be a button that you simply have to push. If you look at your toolbar you'll see two sets of yellow boxes. I think if you click the right one it might go back to normal. I'm not that familiar with inv 3 I've only used 7, 8, & 9. Good luck and if you have any questions feel free to ask me.
