To reproduce:
1. Open user's project in Unity, open scene 0
2. Delete copied texture file in Project window
3. In main camera's Inspector window find Test Normal script's public variable's field (type: Texture2d)
4. In mentioned script's component click Copy

Expected: texture is copied identically (check project view or mentioned script component)
Actual: texture copied is not visually identical

Reproduced in: 5.5.3p3, 5.6.0f3, 5.6.1p1, 2017.1.0b7, 2017.2.0a1

Note: couldn't test on earlier versions - feature wasn't available
Note: visible mismatches of textures (black in project view, blue in inspector selection (script component) and red in inspector's preview
Note: bug results differ across versions (check pictures attached)
Note: switching original texture's type in project view from normal to any other and back to normal turns project view icon black from 2017.1.0b7