Courtesy of inoviridae, I checked up on a potential bug in which factories produced units out a factory essentially free.
The way this works, from what I understand, is that a support factory that is upgraded when attached to T3 mass fabs, when the mass fabs are off, can produce a unit while the mass fabs are off, and upon turning on the mass fabs, the unit gets perhaps "double normal adjacency" and becomes almost free. In the last minute of my 2 1/2 minute replay this is illustrated.