After upgrading to LR4 many of my previews don't show in some of my overlaying folders. It only says that there's no photos in marked folder (don't know the english translation exactly since my version is in swedish). From the beginning I couldn't see the previews in som folders at all but after imprting them they showed up. In some of my overlaying folders (containing folders within folders) I can see all photos but in others not. It's especially annoying in the All photos folder since I can't make an overall search. The same phenomenon occurs when searching on some keywords. Sometimes it says in the metadata-tab in under keyword that ther's no photos but they show up anyway, though in the keywordlist it says the number of photos in the folder. Sometimes no photos at all show up. I have about 65 000 photos in this particular catalogue.