I think what Michael is stating is the other side of the coin on picture display order is achieved. You can use a sort as he states or you can do the explicit set a sort order as I described to override any sort
I guess what we dont see if why your singling out the display of the preview thumbnails sort order on bulkupload. They are not affected by any sort. They are uploaded as noted by simple reading a directory and processing files in order they are found. Same thing does reading an html file. we should go down the file and read every img src tag and grab images. How the server is interpreting the sort order of the directory when we read it I can not say.