Endermen do not spawn in the end if difficulty is set to easy

The bug

Endermen are not spawning in the End easy mode, but will start spawning when the difficulty is raised to either normal or hard.

How to reproduce

1. Reach the end.
2. Set the difficulty to peaceful so that the endermans that have been spawned disappear.
3. Set the difficulty to easy.
4. Note that end does not produce any endermans at this time.