Steps to repro

Notes: Behavior varies in 5.1x to 5.3, however I decided it was not regressive, but by design.

~ There is no definition of what ALT + LMB + Drag/Drop does in the documentation. I personally used it to duplicate to new folder.

Open Unity 5.3bx and open uploaded project.

1. Select 'Texture A' and observe inspector, the texture is set to Normal Map.
2. Do: ALT + Left Mouse Button + Drag/Drop (To another space in project window)
3. Click new copied texture 'Texture A 1'
4. Observe inspector to see Normal map is now "Texture" or "Sprite" in 5.1x

Part 2 : Comparing to materials
1. Create a new Material, we'll call it MatA
2. Drag and drop any texture to Albedo slot.
3. ALT + LMB + Drag/Drop (like before)
4. Observe new material now reverts back to 'white' (empty fields).
5. Duplicate MatA material with Ctrl+D
6. Then ALT + LMB + Drag/Drop MatA
7. Observe New material doesn't reset anymore.
8. Make changes to MatA (Change to a new albedo or set another parameter)
9. ALT + LMB + Drag/Drop MatA
10. Observe new material will revert to previously duplicated material.