The worldspawn breaks and spawns me at Y= -63 if I have the default gamemode set to adventure.

I’ve only tested this in worlds where the game mode is Creative and the difficulty is Peaceful, and commands allowed upon first creating the world. If I then set the default game mode to Adventure after creating the world using the /defaultgamemode command and then die via the /kill command around 1 to 5 times, it eventually spawns me at y = -63. If I set the default game mode back to Adventure, once again using the /defaultgamemode command, it seems to go back to normal. Note that this only affects the worldspawn in my experience, and if I have my spawn set to a bed, it will not put me in the ground unless the bed is obstructed.