Very weird, never seen that either. Depending on how far you are along and how deep the crack is, you can just keep thinning the sapwood until the crack is gone or go the heartwood only route, but I wouldn't trust it. But of course sometimes it's fun to push the limits and see if these things will hold up, I've lucked out a few times with bows I thought were done for and proceeded anyway, and ended up with a shootable bow.