I played against Dark_Horizon today in Tournament Tower, when I noticed something strange. After he has to sell his War Factory, he is still able to build on the top level of the map, after realising he saw my both APC engineers I noticed something was going on. I tried to do the build myself, but I was not able to, as shown in Dark_Horizon-2.JPG. When I was watching back the replay, I also noticed he was putting down a Defense Tower at the top, before he even saw my APC Engineer???
Attached replay and screenshot and also my own attempt.