I’m not sure if this has been mentioned before, but I noticed that when I change the font of the Document Notes window in the Options window, it doesn’t actually change the font. 
Since the Document and Project Notes areas are rich-text, having existing notes convert automatically when you changed the new default font in Options could be massively destructive. The settings in Options will only apply to new documents, just like the formatting settings for the editor. To change existing notes, just select the text and format it directly.