This was definitely fixed for 19.10.
Try the latest themes, either by:
-
Installing the latest
ubuntu-mate-themes
deb package for Eoan (19.10). -
Download a ZIP of https://github.com/ubuntu-mate/ubuntu-mate-artwork and extract
usr/share/themes/
to~/.local/share/themes/
or/usr/share/themes
(as root)
Then "reload" the theme to see the new changes - either by logging out or switching between them in Appearance.