Translucent materials with Modulate blend mode disappear with down-res translucency enabled

Reported from this UDN: https://udn.unrealengine.com/s/question/0D5QP00000MLlco0AD/active-dtr-doesnt-render-beforedofmodulated-materials?fromCase=1

The problem is that, except in very specific circumstances, translucent rendering draws "standard" (alpha blend) and modulate (multiply) materials in the same pass. When a down-res render target is used for translucency, the down-res target is first cleared to black. Since Modulate blend mode multiplies colors, they don't affect the black render target: any color * black = black.

1. Find or create a static mesh with material set to Blend Mode: Modulate, Translucency Pass: Before DOF
2. Run the game and find the mesh
3. Force down-res translucency with `r.SeparateTranslucencyScreenPercentage 50`
4. Expected: Modulate blend mode materials should be visible with down-res translucency