See the .fla and try to replace an image in library with another one. It works fine with export to .swf, but try to save, close and reopen the .fla - all images in the library are same!
Here is the zip contains .fla + "good" .swf, "re-exported" swf and folder with all images. Link -> http://hkultura.com/flash_cs5_bug.zip
None of your library images have extensions. How are your imported images named?