Ipstenu, thank you for your reply:
Do they show up in the view-source?
Yes, when I edit the post, I can see the picture, but it does not show up when I update and view the page.
Have you tried a different theme?
Yes, I use Coraline theme, so I have tried changing to TwentyTen and TwentyEleven, and same result, no image.
Did they work BEFORE you mapped domains?
Not sure, I have installed mapping plugin on a new wordpress install.
I have been spending my time getting my primary domain looking the way I want, so all uploads show up fine in the primary domain.
I have been putting posts on my mapped domains and I did upload new header in the mapped domain, and that all works fine. This is the first time I have tried adding an image into a post, so I am not sure if the problem has always been there or if my recent update to 3.3.2 has changed anything.
Are you using any hotlink protection?
No hotlink protection as of right now.