What is the problem?

When I step on an UPDATE-Block (The dirt block that say "UPDATE!") it causes the game to indirectly crash, Minecraft`s RAM usage spikes up to 90% and higher, taking up all my RAM on my computer, I cannot open my inventory, new chunks do not load, mobs stay motionless (Cannot get damaged, do not look around anymore), I cannot interact with chests, workbenches, furnaces. When I want to exit the world, it gets stuck on the "Saving World. Do not turn off the device." screen. This has happened on several test worlds. Has happened in earlier versions too.

How to reproduce this problem?

1. Start a new world with custom blocks or an add-on with a structure that contains missing blocks .
2. Place custom blocks or load the structure with missing blocks.
3. (Structure method) step on an UPDATE-Block and see the results.
4. (Add-on method) Leave the world and delete the add-on.
5. Load up the world again and step on an UPDATE-Block and see the results.

Edit: As I found out today, this behaviour applies to mobs too. They step on the UPDATE!-Block, they produce the problem described above.