Will you people quit freaking out about things that are more than 8 months old that are rated explicit? At least 1/10th of the images from more than 8 months ago are misrated. Fix the rating and call it a day. It's really not that hard to push "edit, safe, save" honestly.
Actually, I don't think it was locked before. I remember seeing Observing's comment yesterday, clicking the image, setting it to safe and locked, and saving. I guess danbooru locks the rating before applying the change. Filing a bug.