This printing problem occurs if there is a delay feeding paper to the
multi-purpose tray. The lower portion of the image will begin to disappear
about 10 seconds after the Paper Out indicator lights, or about 4 seconds
after the preceding page ejects. The amount of the image affected depends
on the length of the delay. If too much time passes and the image
disappears, the Personal LaserWriter NT will ignore that page entirely and
continue with the rest of the print job.
Because double-sided printing requires feeding paper one sheet at a time,
and because you must wait for the first sheet to complete before feeding
the next, you have little time before the image begins to disappear.
The only workaround is to insert your pages more quickly. Before we
figured out what was really happening, we noticed that the problem
diminished the more we tried to reproduce it. We were getting better at
feeding the paper, and so didn't cause a sufficient delay to see the
problem.