John Carmack praat in zijn .plan over server flood protectie :The demo servers have general purpose flood-protection that has caused some confusion. Clients are only allowed to make one command a second of any kind. This prevents excessive flooding by chats, model / name changes, and any other command that could possibly be exploited. The command streams are stalled, so it doesn't have any effect on processing order or reliability. This means that if you issue two commands immediately after one another, there will be a one second stall before the second command and all movement clears. You see this on the lagometer as yellow spiking up for a second, then dropping away. Hitting tab for the scoreboard sends a command, so you trigger the flood protection if you bang tab a couple times. This has been fixed so that the scoreboard will never send more than one update request every two seconds, but you will need to watch out for it in the existing demo. The defered model loading has also caused some confusion, but that is a feature, not a bug. :-)