This was definitely fixed for 19.10.
Try the latest themes, either by:
-
Installing the latest
ubuntu-mate-themesdeb 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.