Almost any entity inside farmland gets teleported when it turns into dirt

The bug

When an entity has its head inside farmland and the farmland turns into dirt, the entity will be instantly (in less than 1 game tick) teleported above the dirt.

The teleportation works also with entities with NBT NoAI:1. They get teleported up too.

How to reproduce

[e.g. Floor is at y=10]
1. Place a farmland 1 block above the floor. (e.g. x=10, y=12, z=20) [2017-08-28_11.41.47.png]
2. Summon an armor stand on the floor with the head inside the farmland (e.g. x=10, y=11, z=20) [2017-08-28_11.42.23.png]
3. Jump/place a block above the farmland to turn it into dirt. [2017-08-28_11.42.36.png]
4. The armorstand instantly teleported up.

Testing results

• We can teleport an entity with farmland infinite times a tick, but due to the fact that entities can't go through more than a subchunk every gametick, the maximum (upwards) speed is 320m/s.

• Farmland can be transformed by using pistons to move blocks above it, or by moving it below a block, and the bug still works.

• It is possible to build a survival vanilla friendly 320m/s elevator (a subchunk per gametick), moving farmland below signs in the right order.

• Items can be teleported by placing farmland above other farmand using the right update order (this also works at a subchunk per gametick).

• Endermans (3 block high mob) gets teleported using a farmland every third block.

Why it happens (my thoughts)

I think it's a bugfix ended up badly: they tried to fix MC-104259 and they failed.

By the way, it only works with farmland and not with path blocks.
I made a video about to show the bug and to show the testing, HERE (turn on english subtitles).