Shooting through metal doors?

Just witnessed this on a server. Metal door was closed and the player was able to shoot through and kill the other. Is this a bug or hack? Thanks!

It could be lag if you just closed the door

There is a hack that enables you to kill some one through walls and doors.

Funny that this thread is up. My friend was complaining that someone was doing this to him last night and none of us could understand what he meant by ‘shooting through the door’. We just thought he was crazy.

There is a lag related glitch that causes a door not to close client side so they can shoot you but they crash when they try to walk through it.

there are hacks that allows you to shoot through anything