Due to bug in trapper/active.c add_regexp_name() server does not send builder regexps to agent.
Therefore agent is not able to do regexp based on expression in form @expression_name

Fix is actually simple:
zabbix_server/trapper/active.c:

• *regexp[*regexp_num++] = strdup(regexp_name);
  + *regexp[(*regexp_num)++] = strdup(regexp_name);

Please fix it in future releases.

Thank you for good piece of code, anyway.