Duke3D: mirror walls no longer reflect projectiles, breaking existing usermaps
This was an intentional change from commit 22d85479, and it breaks existing Duke3D levels.
While the mirror surface doesn't render correctly if it is not a maskwall, the reflective property is still used by maps. The HOM is usually hidden by another maskwall right in front of the mirror surface.
I attached an example map that demonstrates this. In current builds, the left glass surface no longer reflects projectiles. This has been used in maps made for eduke32 specifically (such as the "Micky Begins" map in the AMC TC).