I just get the same as the old unisub. Where i have to put 2 sheets or 1 sheet folded of parchment paper on my heat press mat for the coasters to sit on and then just 1 sheet ontop of the coasters.
I find if i do not then theres a outline square of colour left on my mat and it stains it and find 1 layer it sometimes goes through so i double it
Ive had no issues with anything else just that
I don't get stains on the back of the coaster if thats what you mean