Player does not spawn on the surface of the world when min_y is greater than 0

The bug

When creating a (flat) world with min_y greater than 0, the player spawns inside blocks (at the lower layers of the world), rather than on the surface.

How to reproduce

1. Select Singleplayer → Create New World → More World Options... → Import Settings
2. Import the 214288.json file
3. Select Create New World
   → The player is spawned inside the ground, rather than on the surface of the world