[RENDERDRAGON] Custom particle materials no longer work

Partner Rank:

2

Partner Team Reporting:

Everbloom Games

Verification builds:

All Render Dragon versions (e.g. 1.16.200.01_rc0 renderdragon)

Summary:

Custom particle materials no longer work

Impact:

We typically use custom particle materials whenever we need a directional particle's culling behavior to be the opposite of what the provided materials do. For example, particles_alpha culls back faces, particles_blend does not (MCM-1252 aside). Sometimes we want a two-sided alpha particle, or a one-sided particles_blend, for which we use custom materials. This bug makes it so we cannot achieve these effects. 
Used in Be a Dragon to make the end-of-level band visible from both sides and now it's only visible from behind. Also used in an upcoming map to make one-sided blend particles, which are now opaque.

Repro Steps:

1. Open the provided world
2. Head to the magenta-floored chunk
3. Look at the cube with a cross in each face. This is made of particles, one for each face, all with a custom material that disables culling.

Expected:

All six sides should be visible at all times.

Observed:

Only the front three sides facing the camera are visible at any one time

Screenshots/Videos attached: Yes/No

Yes

Regression Builds:

Last worked in all DX11 versions