I know this probably isn't much use to you now, but I had the same problem and couldn't find any useful info on how to fix it on-line. I also couldn't find out how to easily remove the knob as it appears to be locked in by a retaining ring. I have now fixed it so for anyone else wondering how to fix this.
After turning off the power, I took the front panel off above the top oven (where the knobs sit) as much as I could (couldn't get it all of without detaching wires), using a head torch I noticed that the control knob has a lug that fits in the groove of the temperature ring. Mine had somehow come out of the groove. Using a flat bladed screwdriver I eased the plastic lug up and turned the selector knob until the lug was within the groove.
Knob now aligns with temperature guide again and goes in and out fully.
H
August 2012