vpnc funciona, mas o network-manager-vpnc falha

Question

Estou tentando conectar-me a uma VPN vpnc.

Eu criei pela primeira vez um arquivo conf /etc/vpnc/clientvpn.conf com esta aparência:

## generated by pcf2vpnc
IPSec ID mygroupid
IPSec gateway some.ip.add.ress
IPSec secret mygrouppassword

Xauth username myusername
Xauth password myuserpassword
IKE Authmode psk

e usando sudo vpnc clientvpn funciona bem.

Agora eu quero usar o plugin vpnc do network-manager. Eu criei uma nova configuração vpn e configurei os diferentes valores:

Eu deixei as configurações avançadas para seus valores padrão. Tentando se conectar do NetworkManager, com os seguintes logs:

NetworkManager[1155]: <info> Starting VPN service 'vpnc'...
NetworkManager[1155]: <info> VPN service 'vpnc' started (org.freedesktop.NetworkManager.vpnc), PID 5888
NetworkManager[1155]: <info> VPN service 'vpnc' appeared; activating connections
NetworkManager[1155]: <info> VPN plugin state changed: starting (3)
NetworkManager[1155]: <info> VPN connection 'clientvpn' (Connect) reply received.
NetworkManager[1155]:    SCPlugin-Ifupdown: devices added (path: /sys/devices/virtual/net/tun0, iface: tun0)
NetworkManager[1155]:    SCPlugin-Ifupdown: device added (path: /sys/devices/virtual/net/tun0, iface: tun0): no ifupdown configuration found.
NetworkManager[1155]: <warn> /sys/devices/virtual/net/tun0: couldn't determine device driver; ignoring...
NetworkManager[1155]:    SCPlugin-Ifupdown: devices removed (path: /sys/devices/virtual/net/tun0, iface: tun0)
NetworkManager[1155]: <warn> VPN plugin failed: 1
NetworkManager[1155]: <info> VPN plugin state changed: stopped (6)
NetworkManager[1155]: <info> VPN plugin state change reason: 0
NetworkManager[1155]: <info> Policy set 'Connexion filaire 1' (eth0) as default for IPv4 routing and DNS.
NetworkManager[1155]: <warn> error disconnecting VPN: Could not process the request because no VPN connection was active.

Não tenho certeza se /sys/devices/virtual/net/tun0: couldn't determine device driver; ignoring... é uma mensagem significativa.

Por que o plug-in nm falha, enquanto vpnc funciona bem?