The standard button to submit a text-only update in BuddyPress says "Post Update" and is located to the lower right of the text box.
When I want to add a photo to the post, that "Post Update" button disappears and is essentially replaced by an "Add photos" button, which is in a different location. From a usability perspective, it is very confusing.
Please make Activity Plus use the Post Update button!!! This is going to confuse the heck out of my users.