My boyfriend had a plastic stent for the jaundice problems when he was first DX'd in April 2007. He had no problems with it for the 2+ months he had it. They replaced it with a metal one before he started chemo and radiation because apparently the plastic stents are more subject to blockage, but he had pain and problems from the day the new stent was put in until he had the Whipple, and it was removed. The doctor had noted a possible mark on his liver and we were concerned with mets, but apparently it looked like th liver had been being rubbed by a piece of the new stent which was causing the problem. I'm not sure if that is your problem, but you might see if they will replace the stent and see if that fixes the problem.
You might also go to the JHU chat board and ask your question there; it is much more active than this one, with a lot more people on it and I usually get good answers really quick there.
http://pathology.jhu.edu/pancreas_chat/