This may sound a little strange, but whenever I bake a pie, the bottom of my pie plate (outside bottom, not baked bottom crust) is very greasy. I use glass pyrex 9 inch pie plates. What is causing the greasiness? The oven? The baking sheet it sits on? I can't figure this out. My fingers are so slick after handling the pie plate, you'd think the fat from the crust was leaching out. Is that at all possible? I thought glass was non-porous. Anyone have any thoughts? Thanks!