I looked a bit closer and found, that in the function
adp_compile_chunk the various new tags should be changed into the
strings that are defined in tag-init.tcl.
They use the function ns_register_adptag, so this should be done
automatically by the funtcion ns_adp_parse. Although the tags are
registered, they are not substituted.
But if you call the .adp-files directly the tags get substituted.