That should be a known bug on a specific teleport that exists on the DM2 map. Not sure if it's also present on "regular" Quake but it's been on QuakeWorld for as long as I can remember.

On the backroom (where there is Red Armor and Mega Health) there is a teleport that goes to the main (BIG) room of the map.

If you jump just before the teleport and "aim" your jump so you go in the top left corner of the teleport, you'll get stuck inside the teleport but not go through until you move a bit.

Also, staying stuck for too long on that teleport during a game, will drown your player, which should definitely confuse your opponent as there is no water deep enough to drown players on DM2.

Good times! Long live QuakeWorld!