In the assignment dropbox, I usually provide detailed feedback to my students in the "Overall Feedback" box.
But sometimes, after I finish all corrections, I would like to add another generic feedback to all, so instead of going back to each and every submition to add the same comment, I use the "add feedback" button .. BUT this action overwrites my individual detailed feedback and only keeps the generic one :( without even a warning :(
So, I suggest that a warning be added, where the instructor is asked if he/she wants to overwrite the existing feedback.