Since cushions can be put in side of incomplete blocks, you can put a cushion inside of a wall block and use it to phase through the wall.

Steps to reproduce

• Step 1: Build a simple wall structure

• Step 2: Place a cushion in any bottom part of the wall

• Step 3: You can then sit on the cushion then un-sit and walk out the other side

Expected result:

You should probably not even be able to sit on the cushion in the first place and not be able to phase through to the other side.

Actual result:

You have a way to quickly phase through walls using the cushion.

Extra info: From what I have seen from the duplicate reports such as MC-309688, placing a seat at the top of the wall ALSO allows you to phase through it. This top phasing could be related to MC-309664 since your hitbox could be inside of the blocks hitbox.

This bug is also kind of game breaking as you can also kind of hide inside of blocks with the cushion with non-block hitboxes like stairs as shown in duplicate report MC-309834 or blocks with full block models but non-block hitboxes such as soul sand and mud as seen in duplicate report MC-309889.