- Build some heat furnaces
- Get them up to temperature
- Build some more furnaces (also some ghosts)
- Some subset of the initial furnaces disconnect from the grid
- After the grid is heated back up to greater than their initial disconnection temperature, they rejoin
It also appears that sticking a single heat pipe onto one of the hot furnaces doesn't connect at all. Sometimes (i.e. I just retried it and it worked that time).