I had this bug many times while playing on servers with the latest 2.4.2 official release; When I get killed and my camera falls down and the scoreboard is displayed on the screen until I press the jump / fire keys to respawn, there are times when if I press jump, fire or the movement keys (not sure which of them) I'm suddenly able to move around like a normal player again (stuck in crouch mode but I move very fast) and without even having a weapon in my hand although I can shoot with some ammo and get killed again.
The scoreboard also sticks to the screen so this is some kind of half-respawn / zombie bug after you die. Usually after I walk around like that for a little while the scoreboard closes and I see a weapon in my hand again, although when this happened once I was still stuck in crouch and moving really fast until I jumped once. This bug also doesn't happen very often so it may take a while until you see it (just keep pressing movement keys or jump soon after you die, not sure which does this)