I see similar issues a lot on frames with extended seat tubes, especially ATBs. Owners raise the post to the point where the bottom of the post is above the top tube. The post is in pure cantilever loading, without the reinforcement provided by the top tube junction. Under such conditions, even with metal tubesets, the failures can be very dramatic. The tops of aluminum tubes will snap off and the steel will buckle, fold back like hinge, and often rupture.