When you place chests down, they wont form double chests. This glitch is quite inconsistent as sometimes it works and doesnt. Im going to explain the steps to reproduce this glitch, but its quite confusing so do look at the pictures attached.

Steps to create glitched chests:

1. Place a chest on the ground.
2. Place chest next to chest on GROUND BLOCK.
3. If step 2 doesn't work, try another area.

Steps to create double chests:

1. Place a chest on the ground.
2. Place a chest by SHIFT-CLICKING the side the the original Chest.

Honestly, this glitch is just very confusing, and kinda gamebreaking as you can also put chests next to doublechests, which was originally not possible. This might/might not work in creative mode.