I wonder if those were extreme angles on bone when they hit?
I know Kurt you said yours was a head shot IIRC?
I remember on another website years ago there was a fella who shot a deer with Barnes bullets that resulted in a nasty splash with very little penetration on the one side and had to shoot it again.
The one thing about it is , like John Barsness ( and many others) have stated ,There is no perfect bullet , they may work 99% of the time, it's that 1% that makes you scratch your head!
Cat