It is apparently not that uncommon and can be repaired with the V-cut Tig weld method. I presently have the same crack on a frame that I am taking to a framebuilder today. When I first noticed the crack, I thought the frame was toast but posted about it as you have. A BF member (scooper) PM'd me that he had a frame with the same crack that he had repaired no-problem. Thanks again BF, get it fixed and ride!