The center of the new pattern now contains both the new block and some of the old pattern.
The result is this new tessellating pattern.
If you are wondering how I knew this was going to happen, the answer is, I didn't. It came as a complete surprise to me. I started playing and there it was.
For more playing with tessellations go to My Posts by Subject in the sidebar on the right and click on Tessellation.
Red and Green OP 4, 5
4 hours ago