I have noticed similar issues... when teleporting into, or out of regions using custom windlight settings... I get a "black sky". Clicking the "Land" button immediately corrects it to the default region setting, but will not change it to a custom altitude setting until I cross the threshold. Also happening to others I know with the same symptoms. This is happening on firestorm 5.0.11... have not tried it on the LL viewer. And it only started last week.