When printing documents that use patterns for filling-in graphic objects, or for lines, the patterns don't appear the same on printouts as they do on the screen. They appear to be solidly filled, or even shaded.
What is actually happening is the dpi (dots per inch) of the fill pattern is getting increased from 72 dpi (on-screen) to the usually higher dpi resolution of the printer. At present, all versions of Windows do not properly handle patterns of sizes other than 8x8. As a result, the pattern shrinks down as the resolution increases, causing it to look shaded or even solid when printed out.
At this time, the only workaround for this limitation is to create your objects in, or paste them into, a paint frame created within your document.