Below layer 0(y=0), structure blocks do not work.
What I expected to happen was...:
I wanted to copy a structure at the 60 layer(y=-60).
What actually happened was...:
I got this error "Unable to detect structure size. Add corners with matching structure names" but the name in each block was exactly the same.
Steps to Reproduce:
1. Make a construction below layer 0(y=0).
2. Place two structure blocks with the corner type.
3. Place one structure block with the save type.
4. The error will appear.
Temporary workaround is to detect the same size box above y=0, then drop the relative position so it captures your creation, then save.