Maybe a bug.

Destroying tile under self on the sky surface will crash server with an error:

5660.563 Error MainLoop.cpp:1202: Exception at tick 10723129: Couldn't find suitable position to put the player in the perimeter of 200 tiles from the point {0.0000000000, 0.0000000000}
5660.563 Error ServerMultiplayerManager.cpp:92: MultiplayerManager failed: "Couldn't find suitable position to put the player in the perimeter of 200 tiles from the point {0.0000000000, 0.0000000000}"
5660.563 Info ServerMultiplayerManager.cpp:776: updateTick(10723129) changing state from(InGame) to(Failed)
5689.320 Info ServerMultiplayerManager.cpp:138: Quitting multiplayer connection.
5689.320 Info ServerMultiplayerManager.cpp:776: updateTick(10723129) changing state from(Failed) to(Closed)

The only entrance to that surface is ~500 tiles from start, and surface is about 10*10.
If player is an admin, he will be respawn as ghost, and could fly around.

I think you removed the ground under the player and it killed the player. There is so floor left in a 200 tile radius so the game can't respawn you. The game assumes this will never happen, because it doesn't happen in vanilla.

I could call this a bug and try to fix it, but I don't think I'm going to bother to be honest.

Just don't kill yourself...