Bests & Worsts Reviews from Amazon

Wanted to buy American and lookedt forward to giving this Presto electric griddle a try. A big selling point was that the grill itself is dishwasher safe. Not! Actually, it is fine if you do not mind the black residue left on the bottom after the dish washing cycle. I do not know what this residue is or where it comes from but it has unnerved me as I am sure it is not particularly good to ingest. That the product is made in China heightens my concern that the recurring residue may be a poisonous substance (i.e., lead) leaching out of the bottom and either getting into the dishwasher, clean dishes, and food. I am now seeing that this residue is a pattern and not from a lack of proper cleaning. Does anyone know what this residue is? I am leaning towards trying to return it and never buying Presto again. It also heats unevenly. Update of 10/20/15: Happened again after hand washing and dishwashing. Photos of each instance are here. Just called Presto which can't explain it although the cs rep said the manual says this happens. I don't see it in the manual. She also said it is a reaction from our water and dishwasher soap. We are on muni water and a fully functioning water softener. No explanation yet from them.