I made a fresh installation of Ubuntu 14.04 and then decided to try Gnome and installed its packages. I didn't like it and came back to using to Unity.
After this experiment the notifications became messed up. For the text messages they appeared in the plain text mode without any borders, in a plain rectangle in the different part of the screen. Also the notifications of the change of volume and brightness are also gone. Where can I restore them? I checked the content of:
[D-BUS Service] Name=org.freedesktop.Notifications Exec=/usr/lib/x86_64-linux-gnu/notify-osd