I don't know what brand you bought, but Silpat is the gold standard.

Check the Cooking forum and post over there. I have never ever heard that there's any aftertaste.

I have off brand baking mats, got about 3 or 4 years ago & not experiencing any problems with them, so I guess I'm no help. I did notice on my package that it said to not use if they got cut. Do you maybe use a metal spatula to pull the cookies off, maybe got slightly cut releasing some type of off taste to them? I was wondering why cutting them would be harmful. I first mistakenly bought a huge mat, thinking I could cut it in half, but then read not to.

Yes, cutting the baking mats is harmful. I bought a set and the instructions state you should discard the mats if they are broken and they should not be used as a cutting surface or used with sharp objects such as knives. I bought the following one. It is FDA approved and does not smell. http://www.amazon.com/Non-Stick-Non-Toxic-Professional-Grade-Silicone-BM-01/dp/B00SLKQ4SI/ref=sr_1_1?s=home-garden&ie=UTF8&qid=1424382558&sr=1-1&keywords=ogeid+kitchen