Just confirmed it - not only did some idiot drive a nail deep into the tree who knows how long ago, but they used a hardened tapered shank masonry nail. Now I don't feel nearly as bad about the performance of the edge - I was pounding the hell out of that thing to get it through there, thinking it was just a big knot. Guest that'll teach me to check out the wood a bit more carefully if I am having problems batoning it.