In Unity, whenever authentication is required and when the PolicyKit authentication agent window is presented, it stays there even after I would enter a faulty password. But under Gnome Shell, whenever I make a mistake, the window is closed immediately. I find this behaviour irritating.
For instance I use Synaptic rather frequently, and I prefer to start it using Synapse. I press Ctrl+Space to invoke Synapse, then I enter "syn" (s-shows SMplayer, sy- shows System Monitor) and than I press Enter so that Synaptic is invoked. Then I'm presented with the PolicyKit authentication agent window. As my password is rather complicated - using special characters and big letters, it's easy to make a mistake. If I do make a mistake while typing my password, I'm forced to redo all the previous steps. It's annoying as hell, knowing that this is not the way the PolicyKit authentication agent window behaves in Unity.