CS5 sort by "Filename" won't hold
Not sure if this is relevant but I noticed, and have been frustrated by the fact that, you can't sort differently for different folders. If you sort images by file type in a folder and then try to sort by date in the next folder, all your folders will re-sort images by date. Whatever sort procedure you select last will be applied to all your folders.
There used to be a way to limit sorts to specific folders but if it still exists, I can't find it.