[exim] router "unseen", and headers_add

Version 4.43

I'm setting up headers_add in router "A", doing an unseen delivery in
router "B" then a real delivery in router "C". The real delivery
doesn't seem to get the headers added. Is this expected?

I've observed it with "exim -bd -d-all+router+transport"
and the sequence seems correct.

The unseen delivery gets them correctly. If I disable "B"
the the real deliver gets them correctly.

Thanks,
     Jeremy