Can't unlock screen if VirtualBox runs in full screen mode

Ubuntu version data:
   Description: Ubuntu 14.04 LTS
   Release: 14.04

Unity package data:

unity:
  Instalados: 7.2.0+14.04.20140423-0ubuntu1.2
  Candidato: 7.2.0+14.04.20140423-0ubuntu1.2

Hello,

I'm running a full updated Ubuntu 14.04 and I've found a problem with the new lock screen (which is otherwise awesome):

When VirtualBox is running in full screen mode, and the screen locks (e.g. i'm away from the computer for a while), I'm first unable to write in the password box in the lock screen, even if the input seems to be focused and the writing caret (I mean, the blinking | ) appears in the input field.

Anything I type in the password box is sent to the VirtualBox's guest OS currently excecuting program, which in my case is usually VisualStudio (I see the password I typed in the currently opened file in VS, as all input is captured by VirtualBox it seems).

To be able to unlock, I need to press RightCtrl + F (which is VirtualBox shortcut for toggling full screen mode) and then I can type in the password input box.

So, although I can use the mouse in the lock screen (as I'm able to click to set the focus in the password box and use the indicators there), it seems that all keyboard input is still captured by VirtualBox.

I haven't tested the lock screen with other full screen applications (such as games) but if you think it's important I'm willing to help testing that.

I think it's a security vulnerability (so I'm marking the check) as the typed password is visible "as typed" in the active application in the guest operating system.

Best regards.