Switch layers ignore "exclude stroke" - bug?

[madrobot]

I'm making a mouth, using switch layers with ASPro auto lip sync (ASPro8.2)

- Group - masked hide all
--teeth - mask this layer
--switch group
---mouths - add to mask, exclude strokes

The mouth masks the teeth so they only show inside the mouth, not past it. It looks right in the workspace window, but on render the "exclude strokes" does not work. So it looks wrong, the teeth cut through the outline of the mouth shape (the lips.)

Pulling a mouth vector layer outside of the switch group and testing again, looks fine in workspace window, renders correctly.

So it would seem that exclude stroke does not work in switch layers. Even though it appears to be fine in the workflow window. Which suggests to me that it SHOULD be working, but somehow does not render correctly.

Anyone had a similar experience, ideas, advice?
(Please, I do not need alternative workflow ideas. I knwo it would work with actions instead of switch, or the mouth as a hole in the face. I need to resolve this issue not avoid it.

It really doesn't make sense. Is there legacy code in switch layers causing an issue? An oversight or gap in the implementation of "exclude stroke" code which ignores switch layers?

Any ideas much appreciated
Adrian