Luma matte isn't working

Hi All,

I'm being asked to tone down a shiny highlight on someone's skin. I did this before using AK's "Blemish Removal" tutorial (using Threshold to isolate the white highlights, then using an adjustment layer below as a luma matte to allow me to help blend/tone down the highlights with various effects). For some reason, the luma matte isn't working. I can isolate the highlights on the face nicely using Threshold, but when I apply the adj. layer as a luma matte below, the effect is gone (isolating the layer above shows just a full white frame instead of the previously black with white isolated highlights).

Any thoughts, or is there a better way to do this?

Thanks,
~Chris