Linking to a .psd with an alpha = no alpha

Not sure if this is a bug or a missing feature.

I have a packed psd file ( actually I have hundreds of them ). RGBA are all used for different channels. But when I link it in Designer and try to separate the channels .. I get no Alpha channel .. I can separate RGB but A is always white.

There's a similar issue in Painter when using theGreyscale Conversion Generator .. it only reads RG and B and ignores the A.