So today came the dracut patch - and it seems to fix it (something). At least I did just reboot and I didn't see the message(s) anymore. The /oldroot is mounted on <pre-shutdown> stage but when I <Ctrl>-d to <shutdown> stage it has disappeared. I copied <pre-shutdown> dmesg to /oldroot/tmp/ but I cannot find it from the /tmp/ now. Is it actually a snapshot? So I think I'll test boot couple of times and if Neil Rickert hasn't encounter issues anymore we can close this.