I am running bbpress(Version 2.5.9) + buddypress(Version 2.5.3) on wordpress version > 4.5.1.
In bbpress there are users with Forum Role as Participant and site role as Participant. I have observed that any participant can delete tags created by any other participant. For example if participant-A creates a topic-A with tag-a, when participant-B replies to Topic-A, then participant-B can see tag-a created by participant-A in tag input field and if participant-B removes it from the input field and submits the reply then tag-a is deleted from Topic-A. I this behaviour normal. I . Any help will be great as I have been trying but could not find any reference to this use case.
To avoid this problem you can simply replace <?php if ( bbp_allow_topic_tags() ) : ?> with <?php if ( bbp_allow_topic_tags() && current_user_can( 'moderate' ) ) : ?> in your child-theme’s form-reply.php file.
This would prevent any non-moderator from gaining access to the topic-tags designation of the parent topic while adding/editing replies.