Structure block lines rendered wrong

OOPS Turns out this was spotted by someone else and I didn't notice, sorry!

 

When saving a build of mine with structure blocks, I noticed that the lines seem to be rendered behind most in-game objects.

 

To reproduce:

1. place a structure block in corner mode
2. place another one, not in line on any co-ordinates of the first
3. place one more in save mode
4. name them all the same thing
5. click detect on the save mode structure block
6. look at water, leaves, or clouds through the lines.