Issue: When running a slideshow on Mirror Show in 10.8, the secondary monitor's display is too large for the screen and hangs off the side of the display. Running the same presentation from the PP slideshow does not result in this problem. This does not occur in 10.6.
Resolution: The issue has been reported to Microsoft support as an issue with Office.
Currently, the workarounds for this are:
1. Run in PresenterView
2. Set up slideshow to "run from kiosk" in slideshow options in PP.
3. Mirror the computer displays, don't rely on PP's mirrored option.