Re-upload submissions changes file extension

[DrOMalley]

Summary: I often have students submit zip files, one item of which is a pdf. To return the work back to the students I really only need to return the pdf. This is close to working but there is an issue with the file type when the file is uploaded back to the gradebook.

Steps to reproduce:

1. Create an assignment, have a test student submit a zip file to that assignment.
2. Download submissions for that assignment. This will result in a submissions.zip file which contains studenttest_3143_207797_zipsubmission.zip for example.
3. The file I would like to return is studenttest_3143_207797_feedback.pdf. Create this pdf file and zip it to upload.zip
4. Back in the grade area choose "Re-upload Submissions" choosing upload.zip. This works successfully and the upload is paired to the assignment correctly.

Expected behavior:

In the "Feedback" I would expect the student to be able to view the pdf file feedback.pdf.

Actual behavior:

There is a pdf icon with the file name zipsubmission.zip in the feedback area.

Downloading this file, it appears to be a corrupted zip, but in fact it is a pdf, which is confirmed by simply changing the extension of the downloaded file to .pdf and the contents are in fact studenttest_3143_207797_feedback.pdf

Additional notes:

I realize this is perhaps not exactly the intent of the Re-upload feature, so perhaps calling this a bug is a loose use of the term, as there are warnings about not changing file names, but it seems like since the system does accept the pdf and file it correctly a minor fix to the file extension would make this work correctly.