This issue has been closed as 'Won't Fix' due to an extended period of time without updates. If this issue is important to you please let us know by posting on the AnswerHub or UDN, and Epic will re-open the ticket for further review.
If you apply the same material more than once as a blendable element the effects will not stack. Only one of the materials will be taken into account. However, if you make a copy and apply that it will stack with the original.
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