It's clearly not just a design error. A conscious design decision was made: build the building with supports in the middle of the sides instead of the corners.

It's clearly not just a design error. A conscious design decision was made: build the building with supports in the middle of the sides instead of the corners. This, in and of itself, was not a bug. In addition, a conscious implementation decision was made: hold the thing together with bolts instead of welds. Similarly, this alone was not a bug. The two taken together hit a corner (heh) case and give rise to a bug.