I built T1 with Soviets and pressed the "S" button for a Sniper squad as soon as it finished building. It finished and the sniper was being built but suddenly the building was destroyed. So I lost my T1 aswell as the manpower for the sniper investment.
I was like
I guess it had something to do with the hotkey for cancelling the contruction of the building still beeing active (it was "S" aswell).
I reported this on the official bug forum months ago.
One game I had a vet3 shock squad with an LMG, shrek and flamer riding around in an M3. (Was a great counter to lone pio squads!)