Interesting... the links are there in the e-mail preview of your message, and they're there in the HTML source of the forum web page too. They just don't show up in my browser (or others' browsers apparently).
Ahh, ok, I think I understand it now. The link you pasted is for a web page, not for the image file itself. The bulletin board software doesn't recognize this, so it emits an <img> HTML tag with the link. But the web browser finds that it gets an HTML page instead of an image file, and of course that doesn't make any sense, so the whole thing disappears. Further, it gets really messed up when one tries to edit the post!
Anyway.. the link, viewed in the post editor window, should look like this (minus the spaces around the square brackets, which I inserted to prevent the bulletin board software from recognizing it as bbcode):
[ IMG ] http://i.imgur.com/gpTiZk6.jpg
[ / IMG ]
and here's what happens:
See the difference? The imgur link formatted for use in the [ IMG ] tag so that it points directly to the source image adds "i." in the server name portion, and adds ".jpg" on the tail.