If a moderator edits a post that already has been edited, and the previous moderator left an edit reason this old reason gets injected into the reason field and with that automatically gets re-used for the new update. This assumes that the post is edited twice for the same reason though this usually won't be the case. I propose to change this behavior to keep the field empty by default, this way if the second moderator doesn't fill out the field the reason at least doesn't contain a reason that doesn't reflect the last change to the post.