Composite Textures Normal to Roughness Alpha doesn't generate valid data

https://udn.unrealengine.com/questions/428429/composite-textures-normal-to-roughness-alpha-doesn.html

1. Create a new material in the editor, open it
2. Add a texture sample node to the graph
3. Slot in a normal map for the texture sample
4. drag off of the alpha channel of the texture sample and add a "DebugScalarValues" node
5. Plug the debug node into base color

Result:
Observe that the value of the alpha channel is over 1.0