Importing multiple SpeedTree assets that use the same texture will not assign correctly

When importing multiple SpeedTree assets that use the same material will cause one to import blank (black) materials and assigned. This happens when importing into the same folder, however, if imported into separate folders and merged will not cause the issue.

This originally worked in 4.7.6 but was broken in 4.8 and 4.9.

1. Open UE4
2. Import the assets attached to this JIRA.
3. Use default settings
4. Import both of the SpeedTree files to the same folder

Result: Textures will not be assigned to the material correctly.

Expected: Textures will be assigned tot he material.