I was composing a reply. In a separate browser window, I found the post that answered the question at hand. I copied the answer's url and attempted paste it into my reply, but it didn't work.
I had to click on the HTML button and paste it into the HTML.
Ed,
I do this kind of copy-and-paste of URLs all the time, so I'm thinking something must be different between your setup and mine to account for the different behavior.
What browser are you using? I'm using IE 7.