The answer is simple: the designer did not think everything through. And the programmer implemented the design without further thought as well.
Most users, while working with computers, think this way: if I do something to make things happen, doing this very same thing again should reverse things. Possibly because such behavior was introduced in computers' UI since the beginning of the web and has been re-introduced over and over again.
The short answer to your question is yes - clicking a clickable element again should revert it to its original state, where applicable.
Long answer — an active element in a UI is there for a user to change its state. Changes of state can be separated into two general groups: 1) the action alters the UI to an irreversible state (for example deleting an item from a screen) and 2) the action alters the UI to a reversible state. Your example is the second case, so users need a convenient way to revert the UI to the original state. This can be done in a few ways, including:
- Click on the element again (which is natural).
- Hit the ESC key (which is a convenient way in computer programs to undo an action).
- Hit anywhere else but on an element (which is a convenient way to close drop-down menus, popups etc.).
- Hitting a "Close" button.
If you create an element which will introduce reversible states, you should also introduce a convenient way for a user to revert the state back. In your case, it could be clicking on the element again.
It is up to the designer to think all these details through and describe the behavior of the UI. After the designer has decided how to revert the UI to its original state, that behavior should be implemented all across the application. Once a user does a series of reversible changes to the UI, he'll expect all other similar elements to behave in the same way. And if they don't, the level of friction and frustration will rise and could possibly lead to abandoning the product and switching to a different program.