How do I completely disable shadows on xfce panel indicators and applications? (Xubuntu 16.04 and compton)

I've recently upgraded from Xubuntu 15.10 to 16.04 and I've noticed that some windows have shadows and some don't (I don't want them). I'm using compton as my compositor with the following shadow related settings in my ~/.compton.conf:

shadow = false;
no-dnd-shadow = true;
no-dock-shadow = true;
clear-shadow = true;
shadow-radius = 1;
shadow-offset-x = -1;
shadow-offset-y = -1;
shadow-opacity = 0.1;

I assume shadow = false; is enough to disable them, the other settings are there as part of my trial and error to see if I could affect the remaining shadows.

The shadows that remain look like this:

They also appear on the Skype and networking context menus, but not on any of the others, including the calendar and user switcher.

In addition to the panel, I'm also getting a shadow on the calculator application, but not on any others that I have tested…

Are these being rendered by compton, or is there something else going on here? If I kill compton, those shadows are replaced with a big block of black, as seen here on the calculator, but this also happens with the indicators in my panel, too:

For default Xfce compositor

Go to Settings -> Windows Manager Tweaks. Choose the tab Compositor and uncheck the option Show shadow under regular windows.

For compton compositor

Add the following lines to wintypes setting in ~/.config/compton.conf

dropdown_menu = { shadow = false; };
popup_menu    = { shadow = false; };

Example:

wintypes:
{
    ## To disable shadows for menus
    # menu        = { shadow = false; };
    dropdown_menu = { shadow = false; };
    popup_menu    = { shadow = false; };
    # utility     = { shadow = false; };
};

Hope you success!

An example for compton.conf in git.archlinux.org