Those are not featured post images, but images that are embedded at the very beginning of posts.
I can see that the problem doesn’t exist when you navigate to the post. The image is nicely floated left and comes before the text in the source. BuddyPress seems to be changing the order of the image and text when it comes to the activity stream display. I’m not so sure that’s a good thing.
You could open a Trac ticket for this requesting that the order of text and images remain the same as they were input in the post form?
