The bug

A hostile mob standing 8 blocks away from a bed (square radius) in the North/West direction (negative coordinates) will stop you from sleeping in a bed, but in the South/East direction (positive coordinates) the distance is 7 blocks

If any zombie moves forward from the green Emerald block to any red Redstone block, the player will not be able to sleep and will receive the message "You may not rest now; there are monsters nearby"

The fix

The distance in the South/East direction (positive coordinates) should be increased to 8 blocks to be made consistent with the North/West distance.