I’ve noticed this same behavior in several of my Rhino v5 files (currently using SR5, but noticed this with SR4 also). I have a curve that crosses over a pictureframe image. When I highlight the curve and hit F10 to display the control points, they are not visible - they appear to be behind the pictureframe image. If I highlight the curve and use either “bringforward” or “bringtofront”, and then hit F10 again, there is no change - the control points are still hidden by the pictureframe image. To determine where the control points are, I have to select a large region around the curve, get the control points highlighted and try to remember their approximate location. Then, I click around in the general vacinity of each control point to finally locate it and move it a bit.
There must be an easier method. How does one get the control points to always be on top of a pictureframe image? Modifying the drawing order doesn’t seem to work.