Can you tell me why I can't edit the link before I post the message, but instead have to wait until it has been posted? I note the code is different.

Don't try and edit links before posting. After you click submit the html code is massaged to add the proper code so the link will open in a new window.

Think about it. You enter a link. The link is just a url. The system (after submit) must examine the url and decide when/if to have it open in a small window. Generally, all links to external sites will be opened in a small window. Internal links in a message will be set to open in small window so you don't leave the message reading process. Internal links in a forum article will not be set to open in a  small window.

All this is necessary only because of high-message-counter tracking when reading messages. We can't have a link in a message opening up a new page in the same browser instance or you can bet the high message counter of users would get screwed up and they would miss messages. So..... EVERY link in messages MUST be massaged after Post is clicked to make the link open in a separate small window.