This bug was fixed in the package initramfs-tools - 0.122ubuntu1

---------------
initramfs-tools (0.122ubuntu1) xenial; urgency=medium

  * Merge with Debian v0.122, known to fix:
    - root=PARTUUID=<partuuid> is not recognized as valid syntax
      (LP: #1531928)
  * Merge with Debian v0.122 (LP: #1541508), remaining changes:
    - Set takeover=1 in update-initramfs.
    - Drop hooks/keymap and associated code; console-setup takes care of
      this in Ubuntu.
    - Add a new 'fixrtc' script that tries to set the system clock forward
      based on the last mount time of the root disk; without this kludge,
      systems without a working RTC will end up in a perpetual reboot loop.
    - Set hostname at boot, for the benefit of mdadm autoassembly.
    - Don't display "Loading, please wait..." message when 'quiet' is in
      /proc/cmdline.
    - Ignore errors from iscan and iscan-data hooks.
    - Allow scripts and hooks to specify OPTION=VAR, and unless VAR is set
      to something other than "n", the script will not be included.
    - Restore the framebuffer hook and script, copying KMS and other
      framebuffer drivers into the initramfs, but make them optional; you
      need to set FRAMEBUFFER=y for these to be included.
    - Add hwaddr= alias for BOOTIF= for compatibility.
    - When receiving "recovery" on cmdline, start upstart with --startup-
      event=recovery (LP: #575469)
    - Make /etc/mtab a symlink to /proc/mounts on startup, since e.g.
      current ntfs-3g doesn't work otherwise.
    - Mount /dev with the default tmpfs size rather than sourcing udev.conf.
    - Automatically blacklist vga16fb when vga= or video= specified on
      kernel command-line.
    - Add Hyper-V paravirtualised device drivers to the initramfs to allow
      booting of stock images in a Hyper-V guest. (LP: #917135)
    - Add mountroot failure support, to allow meaningful messages when no
      root device can be found.
    - Retain netboot= compatibility option.
    - Breaks: mountall (<< 2.0~)
    - Retain cryptopts= compatibility option.
    - Use busybox-initramfs for Depends.
    - Add vfat modules to the initramfs.
    - Maintain compatibility with pre- /run configurations
    - Use gzip from busybox instead of klibc.  Depend on busybox-initramfs
      (>= 1:1.13.3-1ubuntu5) to ensure that we have it.
    - Sync the mount options for /run from /lib/init/fstab (LP: #1152744)
    - Increase rootdelay to 180s on powerpc/ppc64/ppc64el (LP: #1326199)
    - fixrtc: wait for udev to settle to expose device symlinks
    - fixrtc: handle hwclock -s failures safely
    - fixrtc: support busybox, handle last mount time on system partition,
      expose fs create time (LP: #1420473)
    - fixrtc: avoid using xargs, wait-for-root before examining
    - fixrtc: suppress /dev/ram as a root when using systempart (LP:
      #1443329)
    - ppc64el: enable PowerPC NX Crypto Coprocessor
    - resume: only resume when the partition contains a resume image
    - resume: announce resume via plymouth if available
    - Don't load keymaps unless we're loading a framebuffer; but set the
      keymap before giving a root shell.
    - Add new initramfs-tools-bin package containing a binary that uses
      libudev to wait for udev to create the udev device, or wait for udev
      to finish processing if we catch it in the act, and returns the
      filesystem type as already probed by udev.
    - Incorporate rzscontrol from compcache so that we can control current
      ramzswap devices.
    - Support loading compcache from the initramfs.
    - debian/control: update Vcs-* links for Ubuntu.
    - hook-functions: fix PowerPC NX Crypto Coprocessor support (LP:
      #1454687)
    - Drop: Maintain compatibility with pre- /run configurations (LP:
      #1485752)
    - Drop: Ignore errors from iscan and iscan-data hooks (LP: #1485562)
    - init: Mount /dev with "nosuid" Thanks to Daniel (LP: #1450960)
    - import direct archive upload 0.120ubuntu6
    - add squashfs to list of 'most' modules (LP: #1501834)
    - drop Breaks: against upstart as we use it in user sessions.
    - support mounting of loopback devices via loop*= parameters
    - local_device_setup: use wait-for-root if it supports the device
      alias type

 -- Andy Whitcroft <email address hidden>  Mon, 25 Jan 2016 16:08:12 +0000