The bug

Based on 17w50a decompiled using CFR 0_119

It appears the TileTicks upgrader (method b(fm) of the static inner class vt.b) determines the block id of the block to update based on the block at this position. Due to MC-108726 this could cause updates to blocks which did not have an update scheduled before.

The block ids of TileTicks entries could likely be directly updated since there is probably no case where the block id has to determined based on blockstate properties, NBT data or surrounding blocks.

How to reproduce

How to reproduce

1. Download this world and put it in .minecraft/saves.
2. Load the world in the latest version.
3. Teleport to 0, 0.

   /teleport 0 ~ 2
   

   → The dispenser is activated and shoots out the stone item