Incorrect host_name used when nagios_hostname_type is "host"

When deploying the nrpe charm with the nagios_hostname_type option set to "host", the host_name option in the service files in /var/lib/nagios/export is incorrect.

Instead of pointing at the actual hostname, host_name still points at the unit name, as if nagios_hostname_type was still set to "unit" (which is the default, btw):

root@andreas-local-machine-5:/var/lib/nagios/export# ls -la
total 12
drwxr-xr-x 1 root root 224 Jan 8 15:41 .
drwxr-xr-x 1 nagios nagios 12 Jan 8 15:40 ..
-r--r--r-- 1 root root 265 Jan 8 15:41 host__andreas-local-machine-5.cfg
-rw-r--r-- 1 root root 435 Jan 8 15:41 service__juju-mysql-0_check_mysql.cfg
-rw-r--r-- 1 root root 440 Jan 8 15:41 service__juju-mysql-0_check_mysql_proc.cfg

root@andreas-local-machine-5:/var/lib/nagios/export# cat host__andreas-local-machine-5.cfg
#---------------------------------------------------
# This file is Juju managed
#--------------------------------------------------

define host {
    address 10.0.3.77
    host_name andreas-local-machine-5 <----- correct value
    use server
    hostgroups machines,
}

root@andreas-local-machine-5:/var/lib/nagios/export# cat service__juju-mysql-0_check_mysql.cfg

#---------------------------------------------------
# This file is Juju managed
#---------------------------------------------------
define service {
    use active-service
    host_name juju-mysql-0 <---- INCORRECT, should have been andreas-local-machine-5
    service_description juju-mysql-0[mysql] Check MySQL connectivity
    check_command check_nrpe!check_mysql
    servicegroups juju
}

Here is a simple deployer file that shows the problem:
nrpe-test:
    services:
        apache2:
            charm: cs:trusty/apache2
        mysql:
            charm: cs:trusty/mysql
            to: [apache2]
        nrpe:
            charm: cs:trusty/nrpe
            options:
                export_nagios_definitions: true
                nagios_host_context: "region1"
                nagios_master: "10.0.3.75"
                nagios_hostname_type: "host"
    relations:
        - ["apache2:nrpe-external-master", "nrpe:nrpe-external-master"]
        - ["mysql:nrpe-external-master", "nrpe:nrpe-external-master"]