Installation on VirtualBox with a new 18GB btrfs partition fails because of insufficient disk space

I am trying to install Ubuntu 17.04 in VirtualBox with a VDI 18GB fixed size drive on a btrfs filesystem. After partitioning the hdd, choosing country and starting to fill my name the system apparently copies files to the hdd on the background already and fails because of insufficient space.
Update: trying to install again on the same machine, just using ext4 instead of btrfs (choosing the very first default option for automatically partitioning the whole drive). On Ext4 it installs ok.

ProblemType: Bug
DistroRelease: Ubuntu 17.04
Package: ubiquity 17.04.7 [modified: lib/partman/automatically_partition/question]
ProcVersionSignature: Ubuntu 4.10.0-11.13-generic 4.10.1
Uname: Linux 4.10.0-11-generic x86_64
ApportVersion: 2.20.4-0ubuntu2
Architecture: amd64
CasperVersion: 1.380
Date: Sat Mar 11 11:06:04 2017
InstallCmdLine: file=/cdrom/preseed/ubuntu.seed boot=casper initrd=/casper/initrd.lz quiet splash --- maybe-ubiquity
LiveMediaBuild: Ubuntu 17.04 "Zesty Zapus" - Alpha amd64 (20170310)
ProcEnviron:
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 LC_NUMERIC=C.UTF-8
SourcePackage: ubiquity
UpgradeStatus: No upgrade log present (probably fresh install)