Ladders aren't supposed to deal any damage.

However, when ever I descend from ladder on multiplayer, I deals fall damage equal to the amount of blocks the ladders use ( EX: 5 ladders will deal fall damage equal to falling down 5 blocks)

How to reproduce it:
Put a reasonable amount of ladders on a wall (5-10)
Make sure its on multiplayer
Descend from the ladders
You get damaged