This doesn't look like it's a bug necessarily but a horrible design decision. Either way, it needs to be fixed because it makes the browser unusable to people who like to open links in the background. For instance, if I read a Wikipedia article, I often open links in the background so I can read them next when I finish reading what I have open now. That does not work now because as long as a new page is loading, I am not allowed to read the original one.
It is a disaster that the user is not allowed to control what page they want to be on. Imagine a streaming service was interrupting you watching a movie by switching over to some TV show every few minutes.