User Interface in-game function missing.
When you have different units selected, they are displayed on the bottom of your screen. You could see that you are currently selecting for example, 1 hero, 2 sandstingers, and a leviathan. Let's say you wanted to only select that Leviathan, if you click that little icon in the bottom of the screen, it doesn't select him. Nothing happens. I don't think this is an intended design, but a missing feature, as all the other common controls in RTS have been implemented.