Occasionally a new user will post something that needs additional clarification. I ask for clarification and the user posts something new and then posts a comment saying something like "I've added a wireframe that should explain this now." I upvote the comment to acknowledge that I've seen the modification and to thank the new user for improving her post. Later, the comment is no longer relevant and conveys no useful information. I would like to be able to flag it as obsolete, but because I have upvoted it, flagging it is no longer an option.
Feature request: Make it possible to flag a comment that you have already upvoted.