I have been vaping for over a year and have never had this problem. I just got my first 510 and within a day, at 3.7v (not even using a hv mod) the end of the cart (the bottom of the part that holds the filler) has melted. Is this normal? I have never had this happen, not even on a hv mod with a 901 or an 801. Am I doing something wrong?