Why will the clock time not reappear after pressing "clear"? We used the oven at 400 degrees and pressed the "clear" button at end of cooking. We thought the oven was off but later in the evening we realized the oven had not turned off. When I pressed the "clear" button again the oven did turn off but the time display now will not stay as it usually does. We can press the "clock" button and the time will show but the display goes back to 0:00 after maybe 15-30 seconds.