This bug keeps appearing in X3, X7 and now again in X8. Create a graphic in CorelDraw and apply a standard transparent lens to the object, export as a transparent PNG. It should be transparent so when used as a PNG it's a lens.
Currently it is exported as a solid. Time to find my CorelDRAW X5 CDs and install it so I can work on the graphic needed.
If memory serves that docker is a remaining feature of the tug of war between the property bar verses the docker clans.