[exim] Address batching and headers_add

Hi folks,

I'm having a little trouble understanding how address batching in a
transport interacts with headers_add and headers_remove.

Apparently, if I enable batching (batch_size = 10) on my UUCP transport
(pipe driver), headers_add and headers_remove seem to be ignored?

This seems unlikely to me. I'd think that adding and removing headers,
if and only if it made a recipient's copy different from everyone
else's, would simply exclude that recipient from the batch. Is that
correct?

If so, then my headers_add and headers_remove (which are complicated)
aren't being ignored and I'm just making one too many assumptions.

Ciao,
Sheldon.