Hasta La Motion!

In my script (Nuke 5.2v2) I’ve got 3d render layers comped together (all have same alpha and are premultiplied). Downstream from that I have copied my spec layer into a new channel using a copy node. Next I have a grade using spec channel as a mask. connected to the grade is a Sapphire glow v1.01 (source plugged into the grade node).
The issue I’m having is; if I connect the glow before the copy, my alpha is correct (1 where the rgb info is and 0 everywhere else). If I connect the glow after the copy, my alpha is all 1 (white). This is a problem as I am then merging the result over a background.

Is this a bug? Is there a workaround?

Thanks for any feedback!