I'm using Lightroom 3.4.1 64-bit. I put all of my photos into one catalog which know has over 32000 images. In the last day or two, I've started to see a strange problem. When I click on certain directories or collections, the thumbnail displayed is not correct. In some cases, I've had the thumbnail repeated for all of the images in the directory. If I display the image in loupe mode, the correct image is sometimes displayed correctly (and the thumbnail is updated). I'm not sure why this has started happening. It is very annoying and it was very disturbing when I first started seeing it. I thought that the problem was that my catalog was too large, but I've seen reports of other people having catalogs that were 50000 to 10000 images. I've tried to restart Lightroom and to reoptimize the catalog. Neither of these things seems to help.