When I double-click my slides in the Library to add them into the Timeline, why do they appear in reverse order?

When you double-click slides in the Library to add them to the Timeline, each slide is inserted at the current Timeline position. Since the Timeline does not move when you add slides, each slide is added in turn to the beginning of the Timeline - thus, in reverse order of your presentation. If you wish to insert your entire presentation in the correct order, select all of the slides in the Library, then drag them into the Timeline. Alternately, you can add your slides one by one while recording your presentation (i.e.: while the Timeline is moving).