This is not something that is normal behavior for heartbeat. You need to see it as heartbeat being the leading module for displaying activity. So in the case of fbss, shouts, tweets, ... we have to make sure we log the message (with template) in the heartbeat table and heartbeat activity messages will have comments, flags, ... .  The don't add-up as in the question imo. In this specific case, we would make a ilike flag for a heartbeat activity message for the heartbeat streams. fbss flags will only be shown in the fbss stream pages. The reason for this is that both modules have there own tables, with own unique identifiers.

When heartbeat is there, then views lists, fbss views, or other contribs blocks will be the list to use for activity.