I hope I'm not abusing your thread by asking a question that probably has nothing to do with the autosave feature, even as it is about drafts? I have previously begun writing a comment in a thread, but later decided not to post it. Later I have found a link "My Drafts 1" in the box top right, leading me to my unfinished and unposted draft. There are only two buttons, "Save Draft" and "Post Comment". I don't want to do either; I want to abort or delete the draft. Do I actually have to post the draft before I can delete that comment?
Click "My Drafts" in the right-hand column, then click the X to delete the draft.
(Don't post it: only moderators can delete already-posted content.)