I was kind of afraid of that, too bad.
I'm an old maxwell render user and they have different preview scenes to choose from, which I kind of miss. Things like leaf and glass materials simple don't render accurate in the current preview scene and I think it can be a useful feature. The question of course is, how long does it take to develop such a "hack".
If a preview takes a bit longer to render then the Auto Refresh function should be disabled. Also if more advanced preview scenes are available, one could enlarge a preview window and let it render somewhat longer to see the result. If the preview window would update say a few times per second then it would be much more intuitive and useful. This is the same way Maxwell works and it has always worked very well for me. :)
I guess now the only way to accurately edit a material is use it in a full scene, such as an interior scene or the simbal scene (which would also be a good preview scene to have as an option). Maybe I'm not asking for creating custom preview scenes per see but have a few options would be very nice!