TB_London makes sense.
I'm a little concerned by people saying "glue it up and continue." I don't think I'd want to be the one wondering if my Marko knife had a hidden split in the handle.
Weird Wood Pusher
Marko made the right call with replacing the wood.
The crack is following the grain along a medullar ray.
Like when you are splitting firewood.
The split looks a little bit wiggly because the figure is tight compression curl.
This could happen to anyone.
Yep, this looks worse than I imagined, clearly a case for the bin. Too bad, looked like a very nice piece.