Parameters attached to the input of a Vertex Interpolator Material Expression are visible in the Material Instance, even if the output of the Vertex Interpolator Material Expression is not connected to the output.
1. Download the Licensee's test project and open (see addl info URL)
2. Open the Material "/Game/M_Master"
3. Observe that nothing is connected to the final output.
4. Open the Material Instance "/Game/MI_Master"
5. Observe the disconnected parameters are visible and can be edited.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-366229 in the post.