If you stay inside a building with a glass prim. (25% opacity or so)
I noticed that sansar is not render the buildings outside. The transparency seems to work from some light angles you see there's glass.
It's only not good that the buildings you look at from inside true the glass are not visible or get removed from the view.
Now i can remove the glass complete. And possible do that for now. But i don't know if this a know problem.