Transparent decals aren't transparent in DX80 (DirectX 8.0 mode)

[Werewolf]

I need some help with transparent decals in DX80 (DirectX 8.0) mode.

When running in DirectX 9 (the default) they appear fine. However when I load the map onto my testing laptop (which runs in DirectX 8.0 mode), I noticed they keep appearing like this:

The .vmt for that decal is here:

"UnlitGeneric"
{
    "$basetexture" "custom/dr_4halls/decal_trap"
    "$translucent" "1"
    "$decal" "1"
    "$decalscale" "0.25"
    "$nodecal" "1"
    "$selfillum" "1"
    "$ignorez" "0"
}

I feel like I am missing something obvious here because I swear they used to display fine in DX8.0. I could be wrong about that or never noticed, but if there is a way to fix it I'd like to know please. Any suggestions?

 

[Werewolf]

I've just loaded a previous version of this map onto my laptop, as I realised all the decals being effected were new ones I created for this version.

Sure enough, these older decals display properly in DX8 mode. Now I just need to figure out why.