Comment 4 for bug 1713004

This was fixed in initramfs-tools version 0.123 which is available in Zesty and later releases. The fix should be SRU'ed to both Ubuntu 14.04 and Ubuntu 16.04 which are affected. Here's a link to the commit which fixed this:

https://anonscm.debian.org/cgit/kernel/initramfs-tools.git/commit/?id=ac6d31fc2c707b72ff8af9944c9b4f8af303a6a3