Chef Vegabond has picked up two silicon muffin trays a while back. I used one the first time and it worked out beautifully, the second time, the first one I used worked the other stuck. After close examination I saw the one that didn't work had a shinier look to it, I exchanged it and attempted attempt number two. They both stuck. Is it something I'm doing wrong? Do I have to remove the muffins from the trays right away, let them cool completely, 15 minutes? Any feedback is appreciated.