ext4 partition not created as specified

[BertN45]

I have 26GB free at the begin of the drive and create a extended partition in that area and that went OK. While trying to create a 18GB ext4 partition in that extended partition, that extended partition is completely f$$cked up.
See the collage of screenshots in the annex.

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: gnome-disk-utility 3.28.3-0ubuntu1~18.04.1
ProcVersionSignature: Ubuntu 4.15.0-45.48-generic 4.15.18
Uname: Linux 4.15.0-45-generic x86_64
NonfreeKernelModules: zfs zunicode zavl icp zcommon znvpair nvidia
ApportVersion: 2.20.9-0ubuntu7.5
Architecture: amd64
Date: Fri Feb 15 20:14:37 2019
SourcePackage: gnome-disk-utility
UpgradeStatus: No upgrade log present (probably fresh install)

[Sebastien Bacher (seb128)]

Thank you for your bug report, could you also sent it upstream on https://gitlab.gnome.org/GNOME/gnome-disk-utility/ ?
It would be useful to have your journalctl log from around the time you did the change