Web application upload screen has two related usability issues. Maybe I should submit two issue reports, but neither is that big a fix.
If you drag-and-drop a file, you need to hit a certain region of the screen. If you drop it anywhere else, your browser basically wants to open or download the file. The screen layout needs to make it clear exactly where to drop.
If you drag-and-drop an XLS file, the upload silently fails. It should complain about an unsupported file type (you have to convert to XLSX or CSV) just as it does when you use the file upload dialog.