This can even happen with the polyfill batting. My advice: Slow your role. Let the atty cool down a bit if it starts to feel a bit on the warm side. The metal wick technically isn't supposed to be the part of the atty that gets hot. If/when it does, it will start to give a slight burning taste from the polyfill. So if you're sucking on that thing like you're Jenna Jameson in her glory days, you'll end up with a less-than-pleasant taste in your mouth.
I've had my M401 for a little over 4 weeks now and have recently had one atty die on me. Since I was sure it was dead, I tore it apart to check out the design. The heating element is simply a small peice of porcelain with a thin wire wrapped around it. The reason it had stopped working is because there was a layer of charred, black carbon that had built up on the thing. No doubt that added to the bad taste before it crapped out on me. I'm wondering if something like an ultrasonic jewelry cleaner would have gotten that stuff off and saved it.