Every single time you add or remove scenery (no matter what scenery), every time you change/replace a graphics driver... must delete the entire shaders folder and the sim will re-build them on next startup. This ensure that the sim has the most current shader requirements it needs to correctly create the graphics display. Easy to do, but most don't do this hence their graphics distortions.
C:\Users\yourname\AppData\Local\Lockheed Martin\Prepar3D v5\ Shaders << delete the folder. DONE>
Easiest is to just create a shortcut on your desktop to the shaders folder. Then when you want to delete the shaders folder it's just a click/delete/ close the explorer- DONE. Easy as pie. Start your sim and you get updated shaders which are optimized for your current scenery configuration.
Now if you see an issue like this, close sim, delete the shaders - and start up your sim but the new shaders haven't corrected a graphic distortion then it's not the shaders - but something else that is causing the graphical distortion like incorrect layering or bad scenery files!