Routes editing dialog is incorrectly displayed

When I open the routes editing dialog, parts of the window are transparent (see attachment).
That's obviously not by design.

ProblemType: Bug
DistroRelease: Ubuntu 19.10
Package: network-manager-gnome 1.8.22-2ubuntu1
ProcVersionSignature: Ubuntu 5.3.0-17.18-generic 5.3.1
Uname: Linux 5.3.0-17-generic x86_64
NonfreeKernelModules: zfs zunicode zavl icp zcommon znvpair
ApportVersion: 2.20.11-0ubuntu8
Architecture: amd64
CurrentDesktop: MATE
Date: Tue Oct 15 10:29:43 2019
IfupdownConfig:
 # interfaces(5) file used by ifup(8) and ifdown(8)
 # Include files from /etc/network/interfaces.d:
 source-directory /etc/network/interfaces.d
InstallationDate: Installed on 2019-09-26 (18 days ago)
InstallationMedia: Ubuntu-MATE 19.10 "Eoan Ermine" - Beta amd64 (20190926.1)
IpRoute:
 default via 192.168.111.2 dev ens33 proto dhcp metric 100
 10.20.10.0/24 dev ens38 proto kernel scope link src 10.20.10.100 metric 101
 169.254.0.0/16 dev ens38 scope link metric 1000
 192.168.111.0/24 dev ens33 proto kernel scope link src 192.168.111.130 metric 100
IwConfig:
 ens33 no wireless extensions.

 lo no wireless extensions.

 ens38 no wireless extensions.
RfKill:

SourcePackage: network-manager-applet
UpgradeStatus: No upgrade log present (probably fresh install)
nmcli-dev:
 DEVICE TYPE STATE IP4-CONNECTIVITY IP6-CONNECTIVITY DBUS-PATH CONNECTION CON-UUID CON-PATH
 ens33 ethernet connected full full /org/freedesktop/NetworkManager/Devices/2 NAT 52e7dfdb-10e3-3dc1-b53b-c314a602ae48 /org/freedesktop/NetworkManager/ActiveConnection/22
 ens38 ethernet connected limited limited /org/freedesktop/NetworkManager/Devices/3 CPE - 10.20.10.1 984da49a-f0b1-3e7d-8bec-031736b5c2fd /org/freedesktop/NetworkManager/ActiveConnection/23
 lo loopback unmanaged unknown unknown /org/freedesktop/NetworkManager/Devices/1 -- -- --
nmcli-nm:
 RUNNING VERSION STATE STARTUP CONNECTIVITY NETWORKING WIFI-HW WIFI WWAN-HW WWAN
 running 1.20.4 connected started full enabled enabled enabled enabled enabled