Dunster, you are right! I hadn't noticed that. But mitering isn't all that hard, especially if you've ever done a traditional attic windows block. I made two machine sewn hexie tops and the technique is almost identical. You don't even have to get 'exactly' to the marked stopping point. It all presses out fine even if you are a stitch or two away.
The more I look at this block, the more I want to try it. Thanks Gemm, I really needed to add another pattern to my bucket list (NOT!!)