What causes soot from vent free fireplace ,low flame, high flame, dirty orifice, or bad propane? The soot has settle on ceilings ,furniture ,& appliances.
VF appliances must be clean clean clean to burn properly. Get a can of compressed air and blow out the pilot assembly and over the burner and see if it makes a difference. It would be best if you involve your LP supplier in this service work so they can shed some lighten their particular experience with your appliance type.