The bug
Snapshots are loading and saving tile entity data for tile entities that have been destroyed.
How to reproduce
Create flat world with no structures or other entities (optional - for ease of debugging)
Place redstone comparator
Destroy redstone comparator
Stop server
Tile entity for redstone comparator is still saved to the world
This also occurs for at least bed tiles as well. It does not occur for skulls. Other tiles have not been tested.
Related issues
relates to
Comments

Confirmed for 1.13 pre5