This is an unwanted side-effect of
MDL-38555. Steps to reproduce:
- Go to an upload form (e.g. https://qa.moodledemo.net/question/import.php?courseid=2 logged in as teacher).
- Drag a large file into the file manager, and quickly click the "Import" button.
- The "This page is asking you to confirm that you want to leave - data you have entered may not be saved." pop-up appears.
- Click "Stay on page".
- Wait for file upload to complete.
Expected result: you can now submit the form.
Acutal result: the "Import button is disabled".
As a developer, another way to reproduce this is to put a sleep(10) in lib/antivirus/clamav/classes/scanner.php. Saves constandly uploading large files.