It’s weird. Go back to the original place you started the cast, can be a comment or a new cast, start typing, and a button pops up.
Reminds me of a possible bug I meant to tell @dwr - If I click the comment button from the feed, start typing, save the draft, then later go back the persons profile and try to comment again, the draft is not there. I have to go back to the feed and click comment. Is that intentional?
Web client will remember your last cast you haven't sent yet. Single "draft" for now. More improvements coming to mobile and Web clients around drafts soon.