This is the code that is sending the headers & content in 2 different packets.
I've also tried a different version using query_form() from the URI module. With that it is all send as a single packet, but the parameters are then part of the URI and not the content. Can someone confirm if query_form should only be used with GETs?

use HTTP::Request::Common;
use LWP::UserAgent;

$ua = LWP::UserAgent->new;
$ua->request(POST 'http://user:password@z.y.z.com/devicesave.asp',
         Content_Type    => 'application/x-www-form-urlencoded',
          Referer        => 'http://x.y.z.com/newdevice.asp?map=CHI.wu
+p',
         Content        => [
                            'map'                => 'CHI.wup',
                            'CreateNewDevice'    => 'true',
                            'Title'                => 'node',
                            'HostName'            => 'node.acme.com',
                            'IP'                => '127.0.0.1',
                            'PollType'            => 'ICMP',
                            'HostType'            => 'Server',
                            'Info1'                => 'info1',
                            'Info2'                => 'info2',
                            'Snmp'                => '1',
                            'ReadComm'            => 'read',
                            'WriteComm'            => 'write',
                            'OID'                => '',
                            'Logging'            => '1',
                            'Monitoring'        => '1',
                            'StartTime'            => '0000',
                            'EndTime'            => '2400',
                            'Sun'                => '1',
                            'Mon'                => '1',
                            'Tues'                => '1',
                            'Wedn'                => '1',
                            'Thur'                => '1',
                            'Fri'                => '1',
                            'Sat'                => '1',
                            'PollFreq'            => '1',
                            'TimeOut'            => '5000',
                            'DownDep'            => '0',
                            'UpDep'                => '0',
                            'Notes'                => '',
                            'end'                => 'end'
                            ]
                );
[download]