Para 14.04 (Trusty Tahr) ele pode ser desativado com o comando:
gsettings set org.gnome.desktop.wm.preferences action-middle-click-titlebar 'none'
Restaurar estado original:
gsettings set org.gnome.desktop.wm.preferences action-middle-click-titlebar 'lower'
Além disso, as seguintes variantes são possíveis:
gsettings set org.gnome.desktop.wm.preferences action-middle-click-titlebar 'toggle-shade'
gsettings set org.gnome.desktop.wm.preferences action-middle-click-titlebar 'maximize'
gsettings set org.gnome.desktop.wm.preferences action-middle-click-titlebar 'toggle-maximize-horizontally'
gsettings set org.gnome.desktop.wm.preferences action-middle-click-titlebar 'toggle-maximize-vertically'
gsettings set org.gnome.desktop.wm.preferences action-middle-click-titlebar 'minimize'
gsettings set org.gnome.desktop.wm.preferences action-middle-click-titlebar 'shade'
gsettings set org.gnome.desktop.wm.preferences action-middle-click-titlebar 'menu'
Mas o bug ainda está lá, a opção do Google Chrome na configuração "Usar barra de título e bordas do sistema" pode diminuir o impacto ...