The bug

Scheduled block updates are saved in the TileTicks list in chunk save files with their world position instead of an offset within the chunk. This is quite inefficient since TileTicks is per chunk and therefore should only contain entries for this chunk.

How to reproduce

1. Schedule an update for a block outside the area (0, 0, 0) → (15, 15, 15) area (all values inclusive), for example by pressing a button
2. Close the world
3. Inspect the respective chunk in the region file using for example NBTExplorer