Ubuntu – Compton: Incorrect shadow display (favourite settings)

I am experiencing problems with the shadow display of the Compton composite manager. In certain situations, the frame for the shadows exceeds the window it is applied to, leaving a visible border and sort of a transparent box around it.

This seems to occur every time a window or frame overlay is not perfectly rectangular, such as the automatic scroll pointer in Firefox or the addon-menus with little arrowheads on top (please see the screenshot below for reference). There are a few other occasions like these outside my web browser, but I am not able to remember anything in particular at the moment.

Because of tearing issues with my video card, I am required to use Compton as the compositor for my XFCE desktop environment and I have been very happy with it so far, except for the visual issue with these shadows.

I thought that my configuration file might not be set up optimally, I also tried to add the option detect-rounded-corners = true; to it, but that did not make any difference.

Is there a solution to this problem? And are there some good Compton configurations which I could use as a base for my settings in general?

My Compton configuration file looks like this at the moment:

#--------------------------------
#-------Backend Settings:--------
#--------------------------------
backend = "glx";                 # Use GLX backend for rendering
vsync = "opengl";                # Use OpenGL to implement vsync
glx-swap-method = 3;             # Use a triple-buffer
paint-on-overlay = true;         # Improves performance (usually) and reduces flickering
glx-no-stencil = true;           # Improves performance
glx-no-rebind-pixmap = true;     # Improves performance with rapid window changes, might not work with some drivers


#--------------------------------
#--------Shadow Settings:--------
#--------------------------------
shadow = true;                   # Enable drawing shadows on windows
shadow-radius = 8;               # The blur radius for shadows
shadow-offset-x = -8;            # The horizontal offset for shadows
shadow-offset-y = -8;            # The vertical offset for shadows
clear-shadow = true;             # Zero the part of the shadow's mask behind the window, may break some applications
no-dock-shadow = true;           # Do not draw shadows on docks/panels
no-dnd-shadow = true;            # Do not draw shadows on DND windows
shadow-exclude = [               # Do not draw shadows on these specific applications:
   #"! name~=''",
    "n:e:Notification",
    "n:e:Plank",
    "n:e:Docky",
    "g:e:Synapse",
    "g:e:Kupfer",
    "g:e:Conky",
    "n:w:*dockbarx*",
   #"n:w:*Firefox*",
   #"n:w:*Chrome*",
   #"n:w:*Chromium*",
    "class_g ?= 'Notify-osd'",
    "class_g ?= 'Cairo-dock'",
    "class_g ?= 'Xfce4-notifyd'",
    "class_g ?= 'Xfce4-power-manager'"
];


#--------------------------------
#--------Fading Settings:--------
#--------------------------------
fading = true;                   # Enable fading windows during opacity changes
fade-delta = 4;                  # The time between steps in a fade in milliseconds
fade-in-step = 0.03;             # The opacity change between steps while fading in
fade-out-step = 0.03;            # The opacity change between steps while fading out
detect-client-opacity = true;    # Prevent opacity from being ignored for some applications


#--------------------------------
#--------Window Settings:--------
#--------------------------------
wintypes:                        # Change behavior for these specific types of windows:
{
    tooltip = { fade = true; shadow = false; };
};

detect-rounded-corners = true;

I've had another configuration before with which this problem existed as well though.

My hardware is as follows:

     MB  Gigabyte GA-H97 HD3 
     CPU Intel Xeon E3-1231 (No AGP) 
     RAM 32GB DDR3
     GPU Nvidia Quadro 5000 
     2560x1080 Display, 60 Hz, connected via DisplayPort