Usually in Ubuntu any open applications show themselves in Unity with an icon and a tiny white arrow. Multiple white arrows donate an application or window opened several times, e.g. the image on the right shows Thunderbird, Skype and Chrome open.
Active windows have an additional white arrow on the other side of the icon, which once you’re used to it, is quite nice (although give me a horizontal bar any day).
Open applications not appearing in Unity
I’ve noticed though that a few applications, specifically my favourite IDE, gedit, doesn’t appear in Unity with either of these arrows, shown below.
Notice how gedit is clearly open and active in the example above, yet the Unity icon shows neither of the arrows. When this application loses focus, you can’t return it using ALT+TAB either, its just hidden from your sight.
Clicking the Unity icon for gedit again will bring focus to the application, but open a blank new file too, rather annoying.
Scouring the internet it seems this is a rare bug, possibly only effecting Precise Pangolin 12.04 too, but its quite annoying.
Update: I’ve finally tracked down an official bug report on Launchpad, with a recent edit showing its ‘in progress’ which is good!
Unity bug removed by Quetzal 12.10
Update – 4th December 2012. In Ubuntu Quantal Quetzal (v12.10) this doesn’t seem to be a problem anymore. Obviously Quantal isn’t a Long Term Support OS and has only been out a few months, but if the bug in this article is really hampering your work flow then I seriously recommend upgrading your distro.
Will post further information once this Unity bug has been patched or removed.