JavaScript document.domain Uncaught DOMException: Blocked a frame with origin

While I was testing the SOP, i came to this scenario two documents has a relationship with the same domain as i would expected and it throws an error when i try to get the location.

To reproduce the problem:

1. Open https://www.google.com
2. from the console let opened = window.open("https://www.google.com")
3. from the same window do opened.location.toString() which will return the correct location
4. from the second tab's console do document.domain = "www.google.com"

5. from the first tab do opened.location.toString() and you will get an error

   Uncaught DOMException: Blocked a frame with origin "https://www.google.com" from accessing a cross-origin frame.
   at <anonymous>:1:12
   
   

Can anyone explain this strange behavior?

from JavaScript document.domain Uncaught DOMException: Blocked a frame with origin