[arch-general] OpenVPN systemd unit not prompting for password

I have a private key with a password. When I start OpenVPN with the openvpn command, all works fine. When I start it with the systemd unit (e.g. systemctl start openvpn-client@conf_file), a systemd-ask-password process is spawned from the unit but the prompt is not shown. Interestingly, the prompt is shown the I stop the unit. Riccardo Paolo Bestetti