Comment 2 for bug 1733106

I have the same issue.

There are also some unwanted shadows under :
- the Volume OSD
- Brightness OSD
- Firefox's main menu
- windows with unusual shapes (such as dispcalgui start up logo).

To solve these issues, I have added the following rules to the shadow-exclude list in my .config/marco-compton.conf:

"class_g ?= 'mate-settings-daemon'",
"class_g ?= 'mate-power-manager'",
"class_g = 'Mate-panel'",
"class_g = 'Firefox' && argb",
"bounding_shaped && !rounded_corners"

I guess they could be added to the file marco-compton in mate-tweak.