The game's engine is supposed to freeze the player after using the teleporter for 18 tics(half a second). However I have seen some runs where people could go through the teleporter and move immediately after that.
I tried googling this thing up but found nothing. How is this possible?

for some reason, this does not apply if you teleport with the tome of power activated

Mind = blown, would never figure it out on my own. Thank you!