This issue has been mentioned a couple times on the answerhub. None of the threads provide any real insight on the issue at hand. I have made a video of the problem.
What I really want to know (although I didn’t mention it in the video) is if I am doing something wrong. Either with the material setup or with the landscape setup. If it’s not me, I hope you can fix it. The issue is going to cause some problems for development on any project.
Video: - YouTube
A similar thread: Painting: Why is my landscape getting "Corrupt" quads? - Rendering - Unreal Engine Forums
If you need to see my material setup, let me know.