I just recently received the American Weigh Scale (AWS) LB-501 scale. Have not yet used it to make ejuice yet but I was testing it out and found that when I turn the backlight on, it adds 0.15g to 0.20g to the weight even with nothing on the scale. When I turn the light off, it goes back to "normal". So basically the light switch adds weight when it's in the on position. Is this normal or have I received a defective scale?