Hello Henri,
Info from 'Help - About':
Steps to reproduce:
1) be in a region that is running the Magnum RC code on the server. Eg.
http://slurl.com/secondlife/Thorklin/38/157/212) set graphics to Basic Shaders checked, Atmospheric Shaders unchecked.
3) Turn to face west.
4) Go into mouselook and move the camera around.
5) Observe the sky to the west is replaced with a giant black rectangle.
6) Exit mouselook, but move camera around.
7) Observe the sky to the west is still sometimes a giant black rectangle.
8) Move to region that is not on Magnum RC, eg. due west into Frumatay
9) Observe that black sky in the west stops happening
logs & screenshot attached in zip file.
Cheers!