Hi
I have had this problem.
Try the following.
Double click on the Plant Group or edit from the Resource Browser.
Choose to Edit the 2D graphic
Select the graphic (circle or similar) and check the Object Info.
Most likely the shape is being drawn in Layer Plane.
Change this to Screen Plane and use the exit button to return to the drawing.
2D plant graphics should re-appear for any instances of the plant already placed and for any new ones subsequently placed from the Resource Browser.
Hope that helps.
David Kurita-May