I can live with it, just an FYI more than anything else.
I have the "basic editor - simple text box" selected in my UserCP. I have been seeing this popup on every single site navigation or tab/window close for the last week or two. It only get this if the "basic" editor is selected for forum posts. If I change to the "Enhanced Editor" the problem goes away. For inevitable "just use the enhanced editor" posts, that's not acceptable because I cannot stand the in-line attachments that are forced when using the "Enhanced Editor".
