I'd love to be able to find it, but I've looked in the past and come up a blank, but they did a study with it on a bowling machine firing balls down an empty net and there's not much to suggest that it's significantly wrong (if anything I think the results suggested the margin of error with umpires call is too large).
I'd be inclined to say that the issue is more likely an optical illusion caused by foreshortening and the camera angle on TV broadcasts than a widespread failure by Hawkeye.
In this instance, let's not forget the umpire gave it out on the pitch and England went up for it loudly, too, so I don't think it's particularly indicative of a failing of the technology that it showed it smashing in to the stumps.