Custom menus does not show up in menu bar before the menu is activated.

1. Create an Editor script with the following code:
//JS
@MenuItem ("MyMenu/Do Something")
static function DoSomething () {
Debug.Log ("Doing Something...");
}
//end
2. Switch back to Unity and wait for the script to be compiled.
3. Click anywhere in the menu bar.

Actual result: the MyMenu item does not show up in menu bar before the menu is activated.

Expecting the menu to show up when the script is compiled.