Comment 27 for bug 1355453

As I said, it is related to client side decorations. Those are the buttons that are inside the window headerbar. We didn't have those in Luna. This unfortunately is a technical limitation introduced by gtk, we can't do anything about it. Your only option to "fix" this issue would be to disable animations for (un)maximizing, do so by running "gsettings set org.pantheon.desktop.gala.animations snap-duration 0" in a terminal.