This might be because btrfs-progs is not seeded for lubuntu on the install image I get this in the installer.
btrfs-progs: Installed: (none) Candidate: 4.5.2-1 Version table: 4.5.2-1 500 500 http://archive.ubuntu.com/ubuntu yakkety/main amd64 Packages -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1591851 Title: creation of btrfs partition fails during install To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/ubiquity/+bug/1591851/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs