Comment 4 for bug 1641832

I'm having trouble coming up with a simpler test case myself. Here is how you can reproduce with lp:maas-images on Zesty with bash-4.4-1ubuntu1

mkdir maas-images
cd maas-images
bzr init
bzr branch lp:maas-images
cd
export PATH=/home/ubuntu/maas-images/trunk/bin:$PATH
wget http://cloud-images.ubuntu.com/daily/server/zesty/20161111/zesty-server-cloudimg-amd64.squashfs
meph2-build --image-format squashfs-image -vv --enable-di amd64 zesty 20161111 zesty-server-cloudimg-amd64.squashfs out.d

If you execute that with 4.4-1ubuntu1 it fails due to the loop back mount still being mounted(mount | grep maas). If you downgrade to 4.3-15ubuntu1 or use the patch from lp:~ltrager/maas-images/workaround_lp1641832 umount is called and the script executes successfully.