I have a new PB1150 Navigator and after initial burn in, I started the grill on "smoke" as directed. When the smoke dissipated, I set the desired temperature to 225 and the cook temperature shot up to 285 before very slowly going back down to the desired temperature of 225 where it would stay at +/- 10 or 15 degrees. Is this normal or am I missing something. This is my first post and I'm not sure I'm doing this right!