I don't think I've seen this before. The block had a very small fissure on the outside corner, running horizontal wrt the grain. Thought nothing of it, gave it about 3/4" of clearance (plenty I thought) and damn if the thing didn't run right into the pipe....shame because it was a super tight piece.
I scorched the outside just so it would show up.
It's a crack, soaks up stain horribly.... PITA!