It seems there is a bug with PDs that can damage your own ACU!
Here is a reply from a 1 player survival game:
https://replay.faforever.com/16678392
At around minute 9, when an ACU is building a second rows of PDs, you can see that the shots of the PD are damaging the ACU and eventually kill it! This behavior was not observed running a game with the old engine and the same game settings.