Jeff stated in a comment on my answer here that users are allowed to re-flag a post after the initial flag is cleared from the moderator queue (I infer this to mean that you can flag a post as much as you want, but only have one active flag per post at a time, which makes sense).
I've never found this to be true in practice, so of course I had to test it out just to be sure.
I flagged my own answer instructing a mod to clear the flag and post a comment on my answer when that was completed. @Random did this for me. I tried to flag my post again, but got the standard error message:
You have already flagged this post for moderator attention
The button appears after inputting the 10 character minimum, but submitting it after that results in the error message.
So, I'm filing this as a bug report because I doubt Jeff thinks some part of the system is implemented and yet it actually isn't. And because I would really really like to have this ability.