The result is that the cookies setting for whatever tab is currently displayed controls the cookies setting for all the background tabs as well.
If you have a tab in that background that has cookies enabled so that you can be logged into a website, and switch to a tab that doesn't have cookies enabled, it disabled cookies for all the tabs.
If the background tab makes a request, for example, to see if there is updated information, that request will be sent without cookies, which will cause the website to log you out.
The result is that the cookies setting for whatever tab is currently displayed controls the cookies setting for all the background tabs as well.
If you have a tab in that background that has cookies enabled so that you can be logged into a website, and switch to a tab that doesn't have cookies enabled, it disabled cookies for all the tabs.
If the background tab makes a request, for example, to see if there is updated information, that request will be sent without cookies, which will cause the website to log you out.