If the defined work style for the Pandora job is two-sided (either sheetwise or perfector), you can assign artwork to the back side of the layout. Until you do, Pandora adds a dummy step-and-repeat to the back side to show where artwork needs to be placed.
Tip: On the job properties pane, Layout tab, use the transparency sliders for the current and opposite sides as needed to show back-up and alignment of the layouts.