I had that same crack (at the bottom of the head tube) on my Salsa scandium hardtail mtb frame. Pretty much know when it must have happened (fell over from a height) and scandium in addition to being amazingly light, I think may be a bit too brittle to take a lot of abuse. Even so, I wouldn't expect that to occur on my road bike's 6061 alloy frame with it's tapered headset and squoval downtube.