Jamie

Added report using official launcher.

Update: The crash seems to trigger on clicking an item, not just shift-clicking it. Attempting to move a shulker to my inventory crashed the game. I had just disabled all datapacks except [minecart-improvements] as well, so disregard those in the crash report.

After sleeping on it I realized that VanillaTweaks' “More Mob Heads” datapack changes mob drops. After disabling that through commands, the issue was resolved.

What threw me off was that (1) the world this issue came up in did not have any mods or loaders present for the prerelease 2 version and (2) I didn’t think that the datapack rewrote mob drops, only added the chance for a head drop.

I was just made aware that MC-279245 exists and has been closed! Apologies! Thank you all for the hard work you do!

I've been having the same exact issue, except its when I load any world with the C&C Datapack.
I've attached my crash report, as I believe this is the first issue opened on this crash. 

oh its fine now. I assume it was a problem with my laptop

ok I have done so

it just says connection lost, and under it says an existing connection was forcefully closed by remote  host

I am so stupid thank you

In the soul sand one i made it all source blocks yet it doesn't make me go up, but the magma one makes me go down.

UPDATE: I fixed it by opening the GeForce Experience app and updating my graphics card's driver to the latest version. I think you can do this on the Nvidia website if you don't have the app.

Sorry!! And thank you so much 🙂

If you are using Nvidia and the newest Nvidia Drivers then this has been a recent issue and I have had a problem with it. You can fix the issue by going to this link. The link goes to the support page of Nvidia and has a hotfix for the drivers which repairs the bug for minecraft and any other Java based games. http://nvidia.custhelp.com/app/answers/detail/a_id/4378/kw/Minecraft/session/L3RpbWUvMTQ4NzA5NzYyMy9zaWQvazRQNmdlYm4%3D

What graphics card do you have and what Drivers belong to that Graphics Card?

Well, here's the decompiled code from MCP to fix this in 1.9, for Piggies anyways.

public void onDeath(DamageSource par1DamageSource)
{
boolean flag = this.worldObj.getGameRules().getBoolean("doMobLoot");
if (getSaddled() == true && flag == false)
{
this.dropItem(Items.saddle, 1);
}
}

Yep.

I placed the yellow on the duplicated and the red in the same spot on the originals, and when I reloaded they had disappeared.

The world folder is 486 MB when compressed and I can only upload up to 10 MB. What should I do?

these are the best pictures I have of the bug