Had a quick search, and from what I can tell, its something to do with there being a risk of fire? (I'm assuming there maybe chemicals/solvents in stain removers that could be flammable when introduced to heat).
Not sure either? But this is all I could find - this was in a John Lewis tumble dryer manual.
Recently bought a condenser dryer, noted today that instructions state that if you put any stain remover in with your washing load, that before you put into the dryer you must do an extra rinse cycle? Why? What happens if I don't? TIA