Comment 4 for bug 1722534

to be clear, this could arguably be considered a bug (that ifupdown/vlan doesn't correctly handle the magic auto-vlan-id detection for qinq, even if the vlan-raw-device is specified), but as we no longer support ifupdown/vlan, i don't think Ubuntu is the place to fix this; if it would be fixed at all, it should be reported to, and fixed by, Debian.