After I reviewed the source code carefully, I found line 154 in question/engine/datablib.php, "$value->save_files($stepid, $context)" should return the value. So, just simple change the line to:

line 154: $value = $value->save_files($stepid, $context);

Things work as expected. I am not sure this only happens to Oracle or also to other databases.

This bug needs to be tested on Oracle, but it would be good to repeat the tests on a more common database (that is, MySQL) to verify there are no regressions their either.

1. Create a quiz and add two essay questions.
2. The first essay question should allow attachments.
3. The second essay question should use the HTML editor with the filepicker.
4. Attempt the quiz as a student.
5. Attach a file to the first essay question.
6. Embed an image into your answer for the second question.
7. Submit the quiz.
8. As either teacher or student, review the quiz, and make sure the files are all present and correct.
9. Finally, for good measure, as teacher regrade the quiz (using the button in the Results -> Grades report in the quiz navigation). Make sure the files are still present.