So, sometime maybe the server think you are not at the place you see right now. It will move you to another place 1 or 2 seconds after you switched the soldier. And this moving sometime will move you through the wall.
So today, I was killed on stairs, then I switched to my machine gunner. In the camera of my machine gunner, I saw I was on the stairs where the enemy killed me.
I knew he was on the top of that stairs, so I quickly turned around and shot him. And this bug happened at the same time, server pulled me over a wall.
Before I completely went through that wall, I hit and killed him, but the replay only shows that I killed him by shooting through the wall. It really makes me like a cheater.