Prob With Dual Display Full Screen

[Uber Nooblett]

I've recently developed a problem, no Idea how it came about, but for some reason when I want to full screen apps, visualisations or games, they only full screen to one display rather than the whole desktop over both displays. This is pretty annoying for movies, games and visualisations and also when I'm doing gfx work in Gimp as its real hastle to have to drag out the bordered windows each time.

is there a fix for this?

Thanks in advance for all your help