"Registration mail is sent to your e-mail" message doesn't appear in Opera

1. Go to Forum in Opera browser, press "Sign Up" button
2. Enter valid data, press "Sign Up"

As a result, gray screen with no messages is shown (please, see video attached)
Expected result: "Registration mail has been sent to your e-mail. Please follow the activation link in this mail to complete registration." message should appear on a gray background.