My wife and I have both witnessed this also. I watched him/her mining mythril for a while. They're always stealthed, mine a node, then poof disappear and reappear at another node. Several people saw this while I was there and mentioning it in chat got several replies that many had seen this cheater AND reported it days ago. And tonight, I checked the market and sure enough there was stack after stack of HQ mythril ore selling by a person with the same name (minus the space between first and last name) as the cheater that's been porting around mining for days. I reported them. My wife reported them. Several people in chat said they reported them and had done so days before. I really hope SE gets in gear and puts an end to this because this will ruin the economy if allowed to continue. I won't give their name because I don't know if it's against the rules, but if you're on Adamantoise, go to where mythril is mined, you'll see them...if they haven't gone up to the next tier yet, that is.