Bonus Chest Spawning in wrong location.

What happens: When creating a new world with Bonus Chest turned on, With all Experimental switches turned on, the Bonus Chest spawns underground, and not within the 5 blocks around the player spawn.

Observed behavior: The last world I created, the Bonus Chest spawned at Y=9 directly below my character which spawned in water at Y=63. The previous world, the Bonus Chest spawned at Y=8 below my character spawn at y=93.

Expected behavior, the Bonus Chest should spawn around character within 5 to 10 blocks in a specific area from the player as center, and player should always spawn on land as should the bonus chest on the land surface near the player.