What I've read[1][2] in regard to this incident is that it is most likely a calibration issue: i.e. the touch screen is improperly calibrated and as a result is not selecting the proper region of the screen. Now this is concerning because it likely means other machines could be or are miscalibrated. However the important takeaway here is that this is not some malicious attempt to rig the vote. If that were the case the likely method would be completely invisible from the UI; why would an attacker bother to actually show a user they were being manipulated? Of course, they wouldn't.
[1] Joseph Hall comments here, also provides a link to further commentary by him: http://gawker.com/5958114/an-expert-weighs-in-on-that-viral-...
[2] http://www.theawl.com/2012/11/the-truth-about-voting-machine...