This is the save file and here is the location of the occurrence.

Its in the bottom left of the base

http://imgur.com/a/2RWEj

I figured it out.

Either:
I put a blueprint down of my walls, and then placed it myself, and the robots didn't know what to do.
---
When I put the blueprint down, I "shift clicked" certain parts of the wall to continue placing flamethrowers in the same spot, and where the walls were blue the ...

I don't know how to explain it so i couldnt search for it, sorry if its been answered.

youtube /watch?v=N2rFVPydT7E