I have this same problem continually maybe someone has an answer

From incoming text from Heroglyph plug in Vegas I place Boris red plug on that , all my alpha channels in Vegas , Boris and Heroglyph are correct unmated and I still get a sharp alpha edge
After I render the final clip even in the preview the edge is there almost like unsafe color difference that causes the edge

If I switch to a premultiplied channel its worse

Is it because I am overlaying plugins ?