Something wrong with sub-folder function?


I've chosen the directory that contains my all Images D:/Images/, and i've checked the "Include subfolders" option. There is thousands of images in subfolders-in-subfolders in this main folder. However, it took only a few seconds to scan all these images and gave alert that there is no duplicate. For just tesing, I've chosen a subfolder in this main folder, it is still being scanned. A subfolder is taking longer than main folder? Something should be wrong i think?