Scott,
If your neck sizing die and your f/l sizing die are the same brand, try swapping the expander ball on the decapping rod. It sounds to me like the expander on your f/l die is a tad bit too large. If you are handy with tools, you could chuck it up in a drill and CAREFULLY "polish" it smaller with emery paper. I seriously doubt that the cases are work hardened yet. Hope this helps a bit.
Jim