Weight Layers and Alpha Layers on Material create Black areas when Painted on a Landscape

Painting on a landscape layer with both an Alpha Layer and Weighted Layer creates black areas. Per documentation painting with an alpha layer should smooth over black areas when multiple weighted layers are used. However, After painting with both black areas on a landscape still occur.

Project files exceed 50 mb.

Link to Dropbox at bottom of UDN post.

1. Download TerrainProblem49 File
2. Create a new landscape
3. Apply the Material "Test Terrain", located in the terrain folder, to the Landscape
4. Add Landscape Layer Info to all of the paint layers
5. Paint the entire landscape with one of the weighted layers.
6. Paint an area with the "Main" layer
7. Paint around the outside of the "Main" layer with another weight layer that is different than the one populated the landscape layer.

Expected : Complete fill of the landscape where the three layers meet.
Result : Black Squares near edges of landscape grid and edges where material is painted.