Comment 2 for bug 1000569

Today, the 27th September 2015 Anno Domini – about three years after you reported this issue (3,5 years after the linuxmint forum thread you posted) – I was troubled by it, too.
Thank you for posting the resolution, too.
Additionally, I want to mention that I had also an issue with Grub. Maybe it was by an initial faulty editing of mine, but fwiw I want to post the line here, too:
in /etc/default/grub
GRUB_CMDLINE_LINUX="cryptopts=target=$Crypted_Volume_Group,source=/dev/sda2,lvm=$Crypted_Volume_Group"

(sda2 is the location of $Crypted_Volume_Group)

hth