John,
Are you sure you didn't get up and into the shoulder blade?  I guess it's possible a centered rib might stop the arrow but I wouldn't have thought so.  I would have guessed major bone strike to stop the arrow like that...either big leg bone or scapula.  Too bad, you've really a string of bad luck.  I would chalk it up to another Murphy attack and get after it again.  She will almost certainly recover.
By the way, how high up are you?  The higher I go the more I struggle to keep my arrows down.  I have done the same thing, though it was with a steel head.  My shot got up into the spine as the shot was very close and I was high.
George