In the Future missions screen, the "Duration Pie" is normally used for navigation, by setting a desired mission duration, locking it in, and navigating between compatible missions using the standard scrolling methods (graphical/keyboard arrow buttons). For duration missions, the pie does double-duty modifying the duration setting. So while non-duration missions display the set length of that mission, on a duration mission the duration is displayed as whatever duration length the pie was set to when scrolling to the mission.

On a duration mission, I think the listed duration and the mission penalty readouts should both change when the pie is clicked to provide an accurate readout of the duration mission, as the mission is currently configured.