X-ray when inside of stairs

If you make a 1x1 piston door as shown in Mumbo Jumbo's video "Every Piston Door from 1x1 to 10x10" and add blocks at the end it allows you to see through blocks when you go through it.

Steps to reproduce: Use the world download from the specified video and add the edits in the screenshot "Back" to the back of the door.

The screenshot "Before" shows the original piston door without the x-ray glitch edit.