Keyboard focus jumps to the top of the page after uploading a file

Steps to reproduce:

• Create a new Assignment module
• Using the keyboard to tab through the form, enter a title, then open the file manager and select a file.
• Tab to "Upload this file" button and press enter.
• Expected: The file manager is closed, and focus returns to the button that opened it.
• Actual: The file manager is closed, and focus is moved to the top of the page.