Moving my post to join yours...
Ok so I played with this a lot.
I'm calling this the IBB (Instant Build Bug) for now.
Here is an unlisted YouTube video for demonstrations. (Bare with my music, forgot I had Dubstep playing while I recorded...)
https://www.youtube.com/watch?v=2q0-GZWkZUE&feature=youtu.be
I did three different scenarios
Scenario One:
Engineer #1 builds Logistics Array #1
Engineer #1 Ques to build Logistics Array #2
Logistics Array #1 complete, Engineer #1 moves to begin Logistics Array #2
During the build, Metal runs out, but ESC/ESC does nothing at this point
Engineer #1 builds Logistics Array #3
Metal runs out, ESC/ESC begins the IBB
The IBB didn't seem to begin until after I had selected the Engineer and doing the ESC/ESC
Scenario Two:
Begin a map without any metal extractors in game, to speed up how fast you burn through your stored Metal
Engineer #1 builds Logistics Array
Engineer #1 completes the Logistic Array
Engineer #1 builds Logistics Array #2
During the build, Metal runs out, ESC/ESC begins the IBB
The IBB didn't seem to begin until after a certain amount of time had passed. Several ESC/ESC attempts failed both selecting nothing and selecting the Engineer.
Scenario Three:
Engineer #1 builds Research Matrix #1
Que up 5 more Engineers to be built
Engineer #2 appears, and is sent to build Research Matrix #2
Engineer #3 appears, and is sent to build Research Matrix #3
Research Matrix #1 is built
Engineer #4 appears, and is sent to build Research Matrix #4
Engineer #1 sent to build Research Matrix #5
Engineer #5 appears, but I leave him alone
During the builds, Metal runs out, ESC/ESC begins the IBB
No Engineer was selected at this time, or at the time the Metal ran out.
Now I tried having an Engineer selected and not selected. Didn't seem to matter.