Giving this more thought, I realized that we are assuming the clothes dryer is gas. My new bet is that it is an electric dryer. The heating element in an electric dryer will get red-hot, creating the ignition source for the stain protector fumes. The electric dryer will pull the fume-contaminated air through the hot heating element, causing it to burn. The smelly air will then pass through the tumbler(clothes) without the use of a heat exchanger. Mystery solved? 😉