mobspawning in the end

I was in the End and put the difficulty on peaceful. After a few minutes i put it on easy again but the endermans won't spawn. and in the overworld it works fine

What I expected to happen was...:
that the mobs spawn

What actually happened was...:
nothing spawn in

Steps to Reproduce:
1. in the end
2.set difficulty on peacefull
3.than set the difficulty on easy

4. nothing will spawn