A longer post would be required to delve into the suspicions for why this was so difficult. Only time will tell what is true and what is not. In any case, Amanda and Dave did beautiful work and I am very happy to see it in print. Maybe in a few years I can even read the paper again and enjoy it.
http://www.pnas.org/content/early/2015/02/18/1413990112.full.pdf+html