I used the Self Cleaning for the 1st time and now my oven door and edge of the oven at the opening has large black areas like the self-cleaning heat burned the blue enamel off! Is this normal? What can I do about it? I hate to see the beautiful oven turn black and ugly. I had followed the instructions in the manual perfectly. And, yes, I removed the racks. Now I'm scared to use self-cleaning in the future.