I choose some folder from media library in Desktop Media Uploader, picked a file which already exists in media library and I checked "Overwrite existing files with the same file name?"

Originally I have a file, say, D:\Umbraco\media\22334\abc.pdf. I need to replace it with a newer version of file with same file name. But after I uploaded the file nothing is changed, I browsed the file on server and found same old file sitting there.

is there anything wrong?