The current process is:

1. Select File
2. Wait (if larger file or slow connection)
3. "This file has been successfuly uploaded."
4. Now select another file.

However, I have have experienced multiple users who sometimes click "Select File" again too rapidly, before the file has sucessfully uploaded. And a smaller number of users have clicked "Return to survey" too quickly. This has resulted in the loss of a file that users tend to think that they have uploaded. While successfully uploaded files are listed, not all users double-check this.