I have a stoneware large bar pan that I've used quite a bit. It was fine at first but now there's a tacky residue mostly in each corner but also around the edges (not in the middle). It's a greasy sticky residue and I even decided to use soap on it but it didn't help. Has this happened to anyone else? Could it be something I did wrong? And any ideas on how to clean it? Or is this the way it gets seasoned?