Normal tangents aren't recalculated on skeletal meshes with bone transforms when recompute tangent is enabled

Enabling recompute tangents on a skeletal mesh does not recompute tangent normals for translated parts of the skelmesh.

If you add
r.SkinCache.CompileShaders=1
r.SkinCache.Mode=1
r.SkinCache.RecomputeTangents=1 _{Do not access these cvars directly}

to the console variables.ini Recompute tangents will correctly work.

1. Download 4.14 release binary
2. Create a new project
3. Click settings > Project settings Search Skin Cache
4. Enable Support Skincache Shaders Support Compute Skincache
5. Restart the editor
6. Import the attached FBX file with import morph targets enabled
7. Add an instance of the Animation into the editor
8. Turn off cast shadows in the detail panel
9. Open the Skeletal mesh of the imported asset
10. Tick Recompute tangents
11. Click Play Simulate
    Result
    No shadowing occurs (Normals being recalculated) on the first transform part of the animation but it does occur during the blendshape portion of the animation.