You are right, we have to correct our previous statement.
We actually shows progress bar if the file that is being scanned is large ( > 50,000,000 Bytes). This is to show that the scanning is in progress. Without the progress bar, the user may think that it freeze, or not working, because the scanning may take some time to complete.
For small files, for speed optimization, we don't show any progress bar during scanning. Each small file will take very small amount of time to complete, so the user can easily notice that it works.
For uploading, we always show progress bar regardless of the file size. Since internet speed may be unpredictable, uploading small file may also take some time to complete.