|Maybe you have noticed, maybe not, but this is a bug that affects the latest version of Ubuntu. In any case, To see if this error affects you, simply open Nautilus and see if right clicking on any file the popup menu appears with the same shadow shadow that the rest of the menus are applied to it (for example, when selecting the File menu or any other). This error is quite easy to fix. Let's see how ...|
sudo apt-get install compizconfig-settings-manager
2.- Then open it. You can find it in System> Preferences> CompizConfig Options Manager.
3.- Where it says Filter, I wrote window decoration and click on the button that remains whose name will obviously be Windows Decoration.
4.- Once there, in the option Shadow windows, replace Any by:
(type = Tooltip | Menu | PopupMenu | DropdownMenu | Unknown) | name = gnome-panel | name = gkrellm | name = VCLSalFrame
5.- Close CompizConfig and verify that everything works fine in Nautilus. 🙂