Comment 6 for bug 1599214

Ok, so the problem is a difference in behaviour for virtio-console vs serial ports.

For plain x86 serial ports, if there's no client connected to the backend, any data is just discarded.

For virtio-console, if there's no client connected to the backend, it'll refuse to send data, hence we never get to log it either.

What i'm not sure on is whether this is supposed to work this way. The virtio-console device actually provides two separate services - a paravirt serial port and a paravirt interactive console. The paravirt serial port mode, certainly requires this behaviour, but I'm not convinced the console mode should do this.