Halthane

Not a hundred percent sure as the picture is a little blurry but I think that's the result of a bad weld, not a bad frame. It looks like it cracked through the weld and then migrated up into the frame itself. Aluminum actually flexes quite nicely, the only problem is that it tends to stay that way, so in bike frames they have to make it heavy enough that the duty cycle (number of flexes before permanent change occurs) is high enough to prevent the frame from folding up the first time someone sits on it. This causes issue with getting good penetration on the welds as well as some issues with the heat treating at the weld site. My guess would be that they didn't get it warm enough in the ovens when they heat treated it, or some minor contaminant within the weld (why they use carbon dioxide and not helium for this is something I really can't fathom since the cost would be a bout a penny a frame on that scale). Anyways you failure was probably the statistical anomaly. I say ride the new one when you get it.