This issue has been closed as 'Won't Fix' due to an extended period of time without updates. If this issue is important to you please let us know by posting on the AnswerHub or UDN, and Epic will re-open the ticket for further review.
Landscape sections disappear for a very brief time when the player camera clips through foliage quickly.
1. Open Editor (Content examples project)
2. Create New Level
3. Open Landscape menu>Create
4. Adjust landscape using sculpting tool so that changes can be seen.
5. Open Foliage Mode
6. Place actor SM_Dead_Tree in foliage browser
7. Uncheck Uniform Scale
8. Set scale to (x min 4, y min 4, z min 7), (x max 12, y max 12, z max 12)
9. Set density to 1, radius to 200, paint density to .35, and brush size to 8192.
10. Paint foliage on landscape.
11. Press Play in Editor, repeatedly and quickly clip camera through foliage.
Head over to the existingAnswerHub thread and let us know what's up.