It's highly concerning that apparently Bitstamp is showing willingness to manipulate the market given the role they play., because we don't know if there is any real foul play behind the scenes. MtGox once did the same with a similar statement in a press release. I deemed them somewhat more professional than MtGox, but perhaps I was wrong.

At least MtGox have stated that they would disallow their employees from insider trading, but I have not heard anything like that from Bitstamp.