Steps to repro:

1. Open Unity;
2. Create new project;
3. Import attached 'SpeedTreeArtifact' unitypackage;
4. Open 'test' scene;
5. Notice, that there is terrain gameobject with some speedtrees on it;
6. Scroll in the scene view, so that tree shadows are visible in both Scene and Game views;
7. In the Project window go to Assets -> Free_SpeedTrees folder;
8. Select 'Broadleaf_Desktop.spm' in the Project window;
9. In the Inspector increase 'Alpha Cutoff' to any value above 0.7 by dragging the scalebar;
10. In the Inspector click 'Apply&Generate Materials';
11. Scroll in and out in the Scene view.

Actual result:
Graphic artifact appears in the speedtree shadow area on terrain (see attached gif video and actual.png).

Expected result:
Graphic artifact should not appear on terrain after toggling any value of the speedtree model.

Notes:
- Reproducible in: 5.4.0b10, 5.4.0b9, 5.3.4f1, 5.3.3p3, 5.3.2f1, 5.3.1f1;
- Reproducible on both OSX 10.11.3 and Windows 10;
- Also reproduces in in the Game view;
- Also reproduces in Deferred, Forward and Legacy Vertex Lit rendering paths;
- Reproduces for both painted trees and dragged prefabs;
- Doesn't repro when Alpha Cutoff value is below 0.7 (e.g. 0.69).