After going to the End and defeating the Ender Dragon, returning to the overworld brings about some weirdness until you reload the world.

Steps to reproduce:

1. Go to the End
2. Return to the overworld

Side effects:

• Portals no longer work (Nether and End)
• You can't place blocks
• You can break blocks, but if you try to put down a different block in its place it turns back into the original block
• You can't spawn mobs
• You can't collect XP
• If you drop an item it disappears
• Mobs won't pay attention to you
• You can't push mobs around
• Mobs won't make their usual noises, but you can still hear your own noises (block placing/breaking, footsteps, etc.)
• You can still blow TNT up with a flint and steel, but doesn't make the fizzing noise, just the explosion noise. TNT can still blow up blocks.
• The lodestone still works, but it doesn't make a noise
• You can still interact with chests and minecart chests, but again, no sound
• If you try to enter a minecart you get kicked right back out. Same story for boats
• Chat still functions
• The player cannot create new chunks

Temporary solutions:

• Reload the world