I see it as a bit of a chicken and egg situation: you see a company you believe is overvalued, therefore you short it. The problem is that once you do that you become financially motivated to see them fail, even if that wasn't true when you originally shorted them.
I agree with the bias, still there isn't a chicken and egg problem in most cases: You do the research before you take the short position, you only publish the research afterwards. If you are a credible investor, the short position follows from the research, not the other way around.
