windows taskbar not disappearing

sometimes when i open when one of PAO windows, it will stay on top and not let the GW2 window come to front to take windowed fullscreen, so i end up with the taskbar constantly showing.

it sometimes goes away if i move the overlay to the other screen and pull it back, or if i lock it and unlock it, but it's unreliable.

any idea how to fix this permanently?

thanks.