i finally figured out today why my "quick reply" often 'disappears'.
i realised i have been inadvertently hitting the "Compose Reply" button instead of the "Post Quick Reply" button on occasion. It feels natural to enter some text and then hit the green button to the right to submit a post (OK buttons are often on the right of dialogs)
perhaps this could be re-laid out so that the compose button group is above the quick reply panel?
its even more of a pain than just hitting the wrong button - as soon as you go back, your text disappears :\