Partitioner does not edit Partition and then hangs

Testing manual ISO install of Ubuntu-budgie in Vbox VM. Existing partitions were /dev/sda1 18 GB (approx), and /dev/sda5 8 GB (approx).

For the manual install, I intended to use about half of /dev/sda1. However, I got this message:

The test of the file system with type ext4 in partitioin #1 of SCSI3(0,0,0) found uncorrected errors.

If you do not go back to the partitioning menu and correct these errors, the partition will be used as is.

Clicking on "Go back" changes the "Used" figure to 0MB and the partition dialogue then hangs on "scanning disks".

There is also no mention of /dev/sda2 (the extended partition), meaning that there's no possibility of resizing it.

I could then quit the installer and continue booting into the live CD.

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: ubiquity 18.04.3
ProcVersionSignature: Ubuntu 4.15.0-10.11-generic 4.15.3
Uname: Linux 4.15.0-10-generic x86_64
ApportVersion: 2.20.8-0ubuntu10
Architecture: amd64
CasperVersion: 1.389
Date: Thu Mar 8 04:56:49 2018
InstallCmdLine: file=/cdrom/preseed/ubuntu-budgie.seed boot=casper only-ubiquity initrd=/casper/initrd.lz quiet splash ---
LiveMediaBuild: Ubuntu-Budgie 18.04 LTS "Bionic Beaver" - Alpha amd64 (20180307.1)
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: ubiquity
UpgradeStatus: No upgrade log present (probably fresh install)