Another, most probably related, dual screen weirdness: sometimes gnome-terminal (started from gnome-panel menu or launcher) has DISPLAY set to wrong screen number.
I.e. terminal started on screen0 normally has DISPLAY ":0.0", but very often it gets ":0.1". And vice versa. When this happens first time, then usually all following terminals have DISPLAY wrong.
Haven't yet found out the logic/circumstances when this happens. Usually the first terminal on particular screen has its DISPLAY right, but second & all the following terminals have it wrong.
Another, most probably related, dual screen weirdness: sometimes gnome-terminal (started from gnome-panel menu or launcher) has DISPLAY set to wrong screen number.
I.e. terminal started on screen0 normally has DISPLAY ":0.0", but very often it gets ":0.1". And vice versa. When this happens first time, then usually all following terminals have DISPLAY wrong.
Haven't yet found out the logic/circumstances when this happens. Usually the first terminal on particular screen has its DISPLAY right, but second & all the following terminals have it wrong.