Debian 9.3 Stretch Unattended-upgrades not detecting Linux kernel security update by default

All my Debian 9.3 "Stretch" instance is showing a kernel update as being available: linux-image-amd64/stable 4.9+8 amd64 But Default Unattended-upgrades config fails to install kernel security update. My configure of '/etc/apt/apt.conf.d/50unattended-upgrades'

Unattended-Upgrade::Origins-Pattern {
        "origin=Debian,codename=${distro_codename},label=Debian-Security";
        "origin=nginx,label=nginx";
        "site=packages.sury.org";
};

I have to add one extra line:

        "origin=Debian,codename=${distro_codename},label=Debian";

Then the Kernel upgrade got pickup.

Unattended-Upgrade::Origins-Pattern {
        "origin=Debian,codename=${distro_codename},label=Debian";
        "origin=Debian,codename=${distro_codename},label=Debian-Security";
        "origin=nginx,label=nginx";
        "site=packages.sury.org";
};

Reference of the fix for this bug:
https://unix.stackexchange.com/questions/414991/unattended-upgrades-not-detecting-linux-kernel-security-update-by-default
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=886415

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