Comment 8 for bug 1311316

@LGB [Gábor Lénárt] that you don't see input field doesn't mean that you can't type password and unlock the screen.

I was trying to reproduce a bug that some people described about fullscreen YouTube videos showing on top of Unity lock screen. I managed to get once a screen locked which would flash and without text input field visible just like on your screenshot but I just typed my password and unlock normally.