initramfs has duplicate copies of libnss_files on x86_64

I'm not sure why this ends up happening, but

$ dpkg -S `which mkinitramfs`
initramfs-tools-core: /usr/sbin/mkinitramfs

$ dpkg-query --show initramfs-tools-core
initramfs-tools-core 0.125ubuntu9

$ sudo update-initramfs -t -c -k $(uname -r)
update-initramfs: Generating /boot/initrd.img-4.12.0-11-generic

## skipcpio is in the dracut-core package and is required to
## extract a initramfs that has an 'early archive' in it. Such
## a thing would happen if you have installed intel-microcode.
$ rm -Rf x; mkdir -p x;
$ /usr/lib/dracut/skipcpio /boot/initrd.img-4.12.0-11-generic | zcat | ( cd x && cpio -uid )
91209 blocks

$ ( cd x && ls -l lib/libnss* lib/x86_64-linux-gnu/libnss* )
-rw-r--r-- 1 ubuntu ubuntu 47608 Aug 31 17:53 lib/libnss_files-2.24.so
lrwxrwxrwx 1 ubuntu ubuntu 20 Aug 31 17:53 lib/libnss_files.so.2 -> libnss_files-2.24.so
-rw-r--r-- 1 ubuntu ubuntu 47608 Aug 31 17:53 lib/x86_64-linux-gnu/libnss_files-2.24.so
lrwxrwxrwx 1 ubuntu ubuntu 20 Aug 31 17:53 lib/x86_64-linux-gnu/libnss_files.so.2 -> libnss_files-2.24.so

$ ( cd x && md5sum lib/libnss* lib/x86_64-linux-gnu/libnss* )
81c4fbcd350e004f1f59bfa50f9d3769 lib/libnss_files-2.24.so
81c4fbcd350e004f1f59bfa50f9d3769 lib/libnss_files.so.2
81c4fbcd350e004f1f59bfa50f9d3769 lib/x86_64-linux-gnu/libnss_files-2.24.so
81c4fbcd350e004f1f59bfa50f9d3769 lib/x86_64-linux-gnu/libnss_files.so.2

$ grep -r nss /usr/lib/initramfs-tools/ || echo nothing obvious
nothing obvious

ProblemType: Bug
DistroRelease: Ubuntu 17.10
Package: initramfs-tools 0.125ubuntu9
ProcVersionSignature: User Name 4.12.0-11.12-generic 4.12.5
Uname: Linux 4.12.0-11-generic x86_64
ApportVersion: 2.20.7-0ubuntu1
Architecture: amd64
Date: Thu Aug 31 16:52:28 2017
Ec2AMI: ami-000000e4
Ec2AMIManifest: FIXME
Ec2AvailabilityZone: nova
Ec2InstanceType: m1.small
Ec2Kernel: unavailable
Ec2Ramdisk: unavailable
PackageArchitecture: all
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: initramfs-tools
UpgradeStatus: No upgrade log present (probably fresh install)