Probably an old bug, but searching for "fog" and "alpha" shows too many unconnected issues... This is very likely another problem with alpha sorting: non-Windlight fog will "make" non-alpha'ed textures appear in front of alpha textures (even if they come from faces physically "behind" them), as the fog sweeps around the sim. When fog is turned off, the strange effect is not present. See the house to the right (location: Neufreistadt, near the telehub) where triangles from the "back" are shown shimmering in front of the house, and the top of the house, very near to the roof, has become partially transparent all the way back, showing the city walls through it. When the non-Windlight fog moves to another position, the house's façade will be solid and not exhibit any problems in rendering (just like the two houses to the left, which don't show any of the artifacts) Notice that the image posted also shows strange glow issues, also when fog sweeps through them. Glow issues have been reported elsewhere e.g. VWR-9207 and VWR-4214.