Comment 17 for bug 967294

IMO the new behavior is better. The old behavior where the panel would not cast a shadow on maximized windows, even if they loose focus, has usability problems:

For example, if you maximize a window and then open a unmaximized window on top of it that window will now be controlled by a menu bar that's a part of another application window. By adding a shadow there is a clear distinction between the menu bar, that now controls another application, and the maximized window.

This problem becomes even worse if you do the same with some application that has it's own menu bar, such as libreoffice. The libreoffice window now has two menu bars with no distinction which controls what application.