GTK file picker dialogue shows too many mount points

[naught101]

I'm running kubuntu 17.10 beta, and the GTK file picker dialogue (for all GTK apps - e.g. firefox, thunderbird, GIMP, agave) is listing a tonne of useless mount points in the left-most panel:

https://i.stack.imgur.com/TrJYy.png

Is there any way to hide these? Other posts suggest adding commands to /etc/fstab, but none of these mount points are listed in fstab to begin with..

These entries do not appear in the Qt file picker dialogue.

ProblemType: Bug
DistroRelease: Ubuntu 17.10
Package: libgtk-3-0 3.22.19-0ubuntu1
ProcVersionSignature: Ubuntu 4.12.0-12.13-lowlatency 4.12.8
Uname: Linux 4.12.0-12-lowlatency x86_64
ApportVersion: 2.20.7-0ubuntu1
Architecture: amd64
CurrentDesktop: KDE
Date: Fri Sep 8 13:33:19 2017
InstallationDate: Installed on 2017-08-19 (19 days ago)
InstallationMedia: Kubuntu 17.10 "Artful Aardvark" - Alpha amd64 (20170818)
SourcePackage: gtk+3.0
UpgradeStatus: No upgrade log present (probably fresh install)