header_rewrite in 6.2.0 doesn't expand variables properly

We have a header_rewrite.config configured to add some headers for original IP address of requestor.

cond %{SEND_REQUEST_HDR_HOOK}
rm-header X-Box-Original-Ip
add-header X-Box-Original-Ip %<chi>

In 5.1.2 this worked fine. With 6.2.0 the expansion is not happening properly and for the header we get a literal %.

6.2.0: HTTP_X_BOX_ORIGINAL_IP=%
5.1.2: HTTP_X_BOX_ORIGINAL_IP=10.3.18.50