Sadly, it's out of my ability.

I generally prefer the "Waisiewig" (is that even how "WYSIWYG" is pronounced?!

) off, since it's much easier to
not ruin links when I post it.
You'll probably need to quote posts then click on "Preview" in the Quick Reply box; that's the best way to quote posts and reply to them in the Full Editor.
I've modified
only your Quick Reply setting, so that it's on by default and not off. (Which is why you probably will see it all of a sudden.)