@mike80222, when composing a message, the “@” applies to the BuddyPress Nouveau template pack, i.e, the label reads “Send @Username” as opposed to the BuddyPress Legacy template pack that reads “Send To (Username or Friend’s Name)” and I’m not sure why it is not the same for both but, that is current behavior. As to the inconsistency for when suggestions appear or not appear is a puzzle, at the moment.
@stephunique, it is possible to filter the suggested usernames by utilizing the bp_core_get_suggestions filter. If you only want to apply this filtering to messages (compose) then your callback needs to be location aware (what/which page/screen is active/loaded), as well.
