Hostile mobs can climb up ladders don't now if this is a bug or not

Put the summary of the bug you're having here

What I expected to happen was...:
Describe what you thought should happen here

What actually happened was...:
Describe what happened here

Steps to Reproduce:
1. Put a step by step guide on how to trigger the bug here
2. ...make a ladder
3. ...next get a zombie or creepier to follow you and have them at the bitten and hit them then thay will go up the ladders