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.