This is the 3rd UTH i have had to buy! i have a zoo-med 20-30gal UTH on a Newtek rheostat. I dont take the adhesive off of them, I have the UTh inbetween a folded blanket and the glass. And in a few spots the UTH melts or leaves brown burn marks on the paper for the adhesive and breaks. Why is this? should i stick it to the glass?