This morning, when I left the house, my train was fine.  It is under the Christmas tree at the moment, and I gave my sisters permission to run the train if they wanted (Which may or may not have been a good idea...)  I was gone for about three hours, and when I came back, the train did not want to go in reverse.  It would go forward just fine, but it went very slowly in reverse, even when I turned it on full power.  I looked at all of the wires and connections... everything seemed fine.  I flipped the locomotive around, and this time it went in reverse, but since I flipped it, it was still going in the same direction.  When I reversed it so it was going forward, it was very slow, even when I turned it to full power.  I put a different locomotive on the tracks, and it had the same reaction, only, when I turned the power pack to zero, it was still creeping forward until I turned it completely off.  I concluded that it was a problem with the power pack.  Please reply if you have a diagnosis.