This is a common problem with PSE6. A new feature with this build causes elements to lose transparency when dragged up from the Project Bin onto a page. Fortunately, there is an easy work-around:
Instead of dragging the element from the Project Bin up onto your paper, you'll need to drag the ribbon (or other .png element) down onto the paper in your bin. You should have success following these steps:
Open a paper and an element.
Double-click on the element to make it "active" - in the large window.
Now click and drag the element down onto the paper in your bin and release.
Your background paper will be active with the transparent element on top.