Refraction broken when using material function

Licensee has provided a BP workaround

Download the licensee repro here - 

[Link Removed]

View the three materials in the content browser. From the licensee:

__M_RefractionNoMaterialFunction__

_This is just a basic translucent material working as expected.
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__M_RefractionWithMaterialFunction_BrokenRefraction__

_Same material as above but MF_EmptyFunction is added which is just an empty material function which passes through the material attributes.
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__M_RefractionWithMaterialFunction_HackFix__

Again same as previous material but with a "fix" to reset the refraction value after the material function.

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The Minimal_Default map has three spheres added. I would expect refraction to work correctly on all of them but the sphere in the center is missing refraction completely.