Create an assignment with all default settings (file submission)
Create a student, submit a file
As an instructor go to the assignment. You see 1 submission "needs grading"
Click on view all submission. Select filter "requires grading". You see the student submission.
Click on the grade icon in the grade column.
On the new page, download the file (you probably don't need to download to reproduce the issue but it is what I did so I mention it), then without doing anything else, press "save changes"

=> the submission is not listed anymore in "requires grading" (mod/assign/view.php?id=4&action=grading). However the submission is still marked as "needs grading" (mod/assign/view.php?id=4).

Expected result: as no changes were done I would have thought that the grading page would forbid to save changes. But if for a reason we need to be able to press save changes then the submission should still appear in "requires grading"