Windows 8.1 has a new feature that can scale the DPI (Dots Per Inch) of each display differently. This feature is often used to make text and icons larger or smaller on the screen. If this has been enabled on the Main (Presentation) Display, the output from MediaShout will not fill the screen correctly.
Fortunately, the solution to this issue is easy. We've located a simple tutorial that will show you how to change that setting back. Visit the following link and follow the instructions for Option 1, steps 3 and 5.
You will need to log out of your Windows account and then log back in for the change to take effect. Once that is done, MediaShout should display correctly!
Kudos to the good folks at Windows EightForums for posting such a useful tutorial!