Could you please try the following?:
Make whatever mip_binary_proxy object you want and try to render it as you usually do.
Now, say you want to change its texture in the render so you change it and rerender with mip_render_subset lens shader in the camera..., Does it render?.
Not for me, it seams mip_render_subset only render straight objects, not proxies (what a shame).
Could you please confirm that?.
Thanks in advance.