Can't select new wallpaer from alternative directory

[slumbergod]

In Xubuntu 16.04 I could right click on the desktop, select Desktop Settings, and select my own wallpaper from an alternative directory.

In Xubuntu 18.04, I can navigate to my own directory of wallpapers but none are previewed. It doesn't want to remember the location either. If I close the dialog then repeat the steps to get it back it has reverted to the default folder.

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: xfdesktop4 4.12.3-4ubuntu2
ProcVersionSignature: Ubuntu 4.15.0-20.21-generic 4.15.17
Uname: Linux 4.15.0-20-generic x86_64
ApportVersion: 2.20.9-0ubuntu7
Architecture: amd64
Date: Tue May 1 16:59:52 2018
InstallationDate: Installed on 2018-04-27 (4 days ago)
InstallationMedia: Xubuntu 18.04 LTS "Bionic Beaver" - Release amd64 (20180426)
SourcePackage: xfdesktop4
UpgradeStatus: No upgrade log present (probably fresh install)

[slumbergod (slumbergod)]

Ok, solution was to delete everything from:
~/.thumbnails
~/.cache/thumbnails

After the reboot thumbnails were present in thunar and ristretto.
Also the problem with the desktop wallpaper changer seemed to be working too.