You just said it does create lag, and makes them unable to do anything due to the black screen without restarting their client. Then you said its no bug

how is it not a bug if you just said that it DOES work, and yes it is lame, but thats the point. And if they do log out and quit client for the time they are invulnerable, which is more like 10-15 sec btw, then when they log back in they will be forced to warp back to the location( not exact ) of where they were when they logged.
Just because its lame doesnt mean its not an exploitable bug.