net.if.in/out not supported

[Fogelholk]

Hello!

This question seems to have been asked a couple of times without any real answer except changing the numeric from float to unsigned, which is default on the net.if.* on 2.0.3 discovery rules.

Now to the problem I'm having;
This is what I get:

# zabbix_agentd -t net.if.in[eth0]
net.if.in[eth0]                               [u|531405635776]
# zabbix_get -s 127.0.0.1 -k net.if.in[eth0]
ZBX_NOTSUPPORTED

And because of this my Zabbix machine will not find the network interfaces of this Debian (6.0.6) server.
It does however find the net.if on another Debian (Proxmox, 6.0.6) server:

# zabbix_agentd -t net.if.out[eth1]
net.if.out[eth1]                              [u|12046206443499]
# zabbix_get -s 127.0.0.1 -k net.if.out[eth1]
12046206090284

What am I missing here?
Please respond if you need more information about my setup!