Unfortunately it isn't Gala related.
OpenBox -> No error Xfwm4 -> ERROR Gnome-session -> ERROR
Now I really can't figure out who should solve this bug. Moreover, it doesn't seems to be related to the message "In pixman_region32_init_rect: Invalid rectangle passed" as initially thought.
See screenshots
Unfortunately it isn't Gala related.
OpenBox -> No error
Xfwm4 -> ERROR
Gnome-session -> ERROR
Now I really can't figure out who should solve this bug. region32_ init_rect: Invalid rectangle passed" as initially thought.
Moreover, it doesn't seems to be related to the message "In pixman_
See screenshots