it is possible to open Forum Login page and Login pop-up window in one broser's tab simultaneously

Steps to reproduce:

1. Logout if you were logged in and open Forum main page.
2. Right click on "Sign In" button and open Login page in a new browser's tab.
3. Open tab with Login page and click on "Sign In" button.

Actual result: Pop-up Login window opens.
Expected result: Pop-up Login window should not open. "Sign in" button on Login page should be inactive.