Interesting. I was just going to add something to my reply to you, only seconds after submitting it, and the Edit Message link wasn't there. Odd.
Anyway, what I wanted to add is that if the problem is with pasting a URL, that's a bug in the site. I know for certain that PM's don't like it if you put in a URL as the first thing, and it wouldn't surprise me if public messages had the same problem, as I suspect (without really looking) that it's a problem with parsing out the "subject" part of the message and stuffing it into a field of a specific size.
If you ever get an error message when submitting a post that starts with a URL, try inserting some text on a line before the URL.