[exim] Visibility of content scan variables

Hello

I am trying to use the $spam_* variables in an exim transport (exim
4.82). But it works only for $spam_score_int.

I have this in my transport config:
  headers_add = \
                  X-Spam-Score: $spam_score\n\
                  X-Spam-Score-Int: $spam_score_int\n\
                  X-Spam-Level: $spam_bar\n\
                  X-Spam-Report: $spam_report

The delivered email looks like this:
X-Spam-Score:
X-Spam-Score-Int: 55
X-Spam-Level:
X-Spam-Report:

The manual says: "These variables are saved with the received message,
thus they are available for use at delivery time." So why can I use only
$spam_score_int?

For now, I have found a workaround. I save the $spam_* variables into
ACL variables, which I can use in the transport.

But I don't understand why this doesn't work. Can you give me a hint?

Sincerly
Johannes