BuddyPress.org

the answer to the first part is that this is a consequence of using Ajax and a good reason not to use it frankly – Ajax is loved because it seems cool and indeed is to a large extent but it is really something that was never meant to be, the browser is not meant to be able to directly pass data to and from the server side, in effect what happens is that the browser doesn’t really now anything has happened and can’t keep a history state thus your back button does not go back one page as that page was never loaded by the browser or requested, hitting back button simply takes you back out of the members page altogether regardless of what page depth you had loaded. For page lists like this my personal view is it’s better not to use Ajax to load in the data.