Cela apparaît quand on fait : gedit unfichier.txt ...
admlho@admlho00:~/Bureau$ gedit Nouveau\ document
(gedit:13334): Gtk-WARNING **: GtkScrolledWindow 0x1a61880 is mapped but visible child GtkScrollbar 0x1a6cb40 is not mapped
(gedit:13334): Gtk-WARNING **: GtkScrolledWindow 0x1a61880 is mapped but visible child GtkScrollbar 0x1a6cd40 is not mapped
(gedit:13334): Gtk-WARNING **: GtkScrolledWindow 0x1a61880 is mapped but visible child GtkScrollbar 0x1a6cb40 is not mapped
(gedit:13334): Gtk-WARNING **: GtkScrolledWindow 0x1a61880 is mapped but visible child GtkScrollbar 0x1a6cd40 is not mapped
(gedit:13334): Gtk-WARNING **: GtkScrolledWindow 0x1a61880 is mapped but visible child GtkScrollbar 0x1a6cd40 is not mapped
(gedit:13334): Gtk-WARNING **: GtkScrolledWindow 0x1a61880 is mapped but visible child GtkScrollbar 0x1a6cb40 is not mapped
(gedit:13334): Gtk-WARNING **: GtkScrolledWindow 0x1a61880 is mapped but visible child GtkScrollbar 0x1a6cd40 is not mapped
(gedit:13334): Gtk-WARNING **: GtkScrolledWindow 0x1a61880 is mapped but visible child GtkScrollbar 0x1a6cb40 is not mapped
(gedit:13334): Gtk-WARNING **: GtkScrolledWindow 0x1a61880 is mapped but visible child GtkScrollbar 0x1a6cb40 is not mapped
(gedit:13334): Gtk-WARNING **: GtkScrolledWindow 0x1a61880 is mapped but visible child GtkScrollbar 0x1a6cd40 is not mapped
(gedit:13334): Gtk-WARNING **: GtkScrolledWindow 0x1a61880 is mapped but visible child GtkScrollbar 0x1a6cb40 is not mapped
(gedit:13334): Gtk-WARNING **: GtkScrolledWindow 0x1a61880 is mapped but visible child GtkScrollbar 0x1a6cd40 is not mapped
(gedit:13334): Gtk-WARNING **: GtkScrolledWindow 0x1a61880 is mapped but visible child GtkScrollbar 0x1a6cd40 is not mapped
(gedit:13334): Gtk-WARNING **: GtkScrolledWindow 0x1a61880 is mapped but visible child GtkScrollbar 0x1a6cb40 is not mapped
(gedit:13334): Gtk-WARNING **: GtkScrolledWindow 0x1a61880 is mapped but visible child GtkScrollbar 0x1a6cd40 is not mapped
(gedit:13334): Gtk-WARNING **: GtkScrolledWindow 0x1a61880 is mapped but visible child GtkScrollbar 0x1a6cb40 is not mapped
Il suffit de réinstaller les paquets :
synaptic
overlay-scrollbar overlay-scrollbar-gtk2 overlay-scrollbar-gtk3
... et il semble que l’erreur disparaît.