I have a problem with 12.04. LibreOffice icons in Unity behaves strange when I'm opening Office files via Nautilus. I have two of them. First both Word and Excel documents is shown with gray Libre icon. When I see this icon I cannot navigate to that document with "ALT+TAB" also I cannot recall that document if I have minimized it. I can reach such documents only when they are visible behind other windows. Clicking on this icon do not do anything.
Second I have a space between opened documents icon in Unity and other icons. In this case I can minimize and hide document and it is still reachable via its icon in Unity (just that space is annoying, also it is much less common for me)
If I open blanc document it works fine.