Actually - maybe not - I was testing wrong (I re-zipped the files as a tar.gz instead of a zip). It is working for me - I'll test on the QA site and report back.
Testing and QA
Yes - it works fine on the QA site.
I'll describe how I tested here:
Step one - Create a new assignment with "File submissions" and "Feedback files" enabled.
Step two - Login as a student and upload a file submission to the assignment (I uploaded a Libre Office document).
Step three - Login as a teacher and "Download all submissions" (From the drop down menu above the grading table).
Step four - Extract all the files from the zip to a new empty folder (Should only be one)
Step five - Edit the document (I added lots of comments) and save it
Step six - Select all files in the folder and create a new zip file from them. (Do not just zip the folder)
Step seven - Choose "Upload multiple files in a zip" from the drop down menu above the grading table
Step eight - Upload the new zip file
Step nine - You should see that there is one new feedback file - click "Confirm" to save the files.
Step ten - Verify that one student received a new feedback file and it is the correct file.
Thanks Damyon - I will give this another go later today. I wonder if my stumbling blocks were your steps 4 and 6 - if I zipped this in a different way? Back later
Got it! It's all to do with how you zip them up - very important to document, so I will, after lunch
That's great Mary - the zip file you upload should basically be in the same format as the one you downloaded (you can even just add or edit files in that zip and re-upload it).
Good to know how it works. But it would also be useful if Moodle could test if the folder as been zipped, and search files there in the zip (avoiding people who zip the folder to have problems).
Cool if it can be done for 2.4, or to keep in mind for 2.4.1
The folders will not be recreated in the zip - you will just get a list of all the files for that student whether they were in a folder or not.