I see this a lot lately and I'm 99% sure this is what's going on:
A player parks their toon and a mat node so the "Interact with Environment" key is displayed. At that point they start executing a macro that continually presses the interact key in an endless loop. Sometimes you can just ignore them and take the mat. Other times you'll get a message stating someone else is using that even though the mat is displayed and the person doesn't appear to be actively harvesting it. Each time I see this I ether just stand there or message the person until they eventually return to their computer, freak out, jump on their mount, and ride away.
I've thought about reporting the player (always seems to be the same one) but I'm not sure it this would be considered a bot..or just bot-like behavior that, while annoying, really doesn't violated any rules.
Any thoughts?