Lettering on glass confusion..

I guess I don’t understand what I’m doing wrong and could use a little help…

I’m shooting an animation through a glass window that has lettering on it. Objects on the other side of the glass are moving. I am using Vector Blur, but because the moving objects are behind the stationary glass, it does not allow the motion blur to be calculated.

So I have split the scene into two render layers, one for the moving blurred background objects and one for just the glass. I hoped I could just overlay the glass layer over top of the moving objects.

It does work…kinda’… but there is a further problem. The lettering, which has a white stroke outline and black interior fill, will now only show the white outline.

Let me show you…

Here’s a small part of the Transparent.PNG used for the lettering (it has a white outline, black fill, and transparent surround:

While here is a one layer pass in action…

But when I set up the two render layers, and composite them together using a MIX shader set to ADD, this is what happens…

So, what can I do to make this idea work? I’ve fiddled with everything I can think of… modes, noodle order, etc. but no go. Is this even possible?

Any ideas would be appreciated.