I don't have any hanging problems in the material editor (PC) for either function or variables. But one quirk I've run into that might relate to this, is that if you are loading a very large image (for the Color, Bump, Transparency, etc.) the image will take a very long time to load up and meanwhile, Vue appears to hang. Once loaded, however, things usually go okay after that. So I'd suggest checking the amount of bytes of your alpha map image. If it's half a meg or larger, that is probably what's causing the hang. And too, if it's that huge, you should be able to remove a ton of bytes by converting it to GIF and reducing the colors to 2 (black and white). That's all a transparency map needs, most usually. Hope this helps! :)