Isn't that the range hood vent? The tabs are to keep it closed when traveling otherwise yes, you are supposed to open them if you intend to use the stove top/oven. My toaster would set off the smoke detector if I didn't run the range hood vent but never did using the stove or oven set off my CO detector if I didn't run the range hood vent. I am not sure your problem is truly solved....future use will tell. How close is the oven to the CO detector? Mine is 10 feet away, so maybe it is a proximity issue. They are quite sensitive.
