I think it's because you're adding attachement or a link to your feed.
As per http://developers.facebook.com/docs/fbjs/streamPublish/
they say :
Updating a User's Status
You can use this method to simply update a user's status. When you do so, the status message appears at the top of the user's profile and on the Friends > Status Updates page. The message also appears in the stream with your application icon.
To use this method to set a user's status do the following:
* Do not include an attachment or action link. If you do, the story will get published and will appear in the stream and on the user's Wall only. It won't appear at the top of the profile or in the Status Updates page.* Make sure the message is no longer than 420 characters. Otherwise, an error gets returned.