Mine does this a little, but only when the clutch pedal is out, and mostly only when it's cold out. I don't think it started before I had some master cylinder issues, though...
We had some -20 degree temps last winter, and suddenly my clutch was slipping, and before I knew it, I could sit in one place idling with the truck in gear, clutch out, no movement. It would stall if I put the clutch in. Couldn't shift with the clutch in. I finally limped it home by pushing the clutch in as far as I could...with it pushed in, the truck would creep forward. Master cylinder fixed this, for reasons I still can't figure out, but maybe I was getting air in the fluid or something and creating some kind of vacuum...I just really don't know.
Ever since then, when it's cold out, I start the truck, let out the clutch (in neutral), and the truck starts creeping forward a bit.
Not sure if this has anything to do with your issue, but I could it could trigger some "eureka!" moment for someone...
