Apparently, when using the iOS Facebook app, it shoves things you're in the middle of reading down and out of view, so it can show you a sponsored post instead.
If that's what comes with an update, you can keep it. Being able to see avatars isn't worth letting FB advertise to me even more. (As if anyone buys anything because of a Facebook post! What jerks.)
Yet another reason on an ever-increasingly huge pile of reasons I love my Playbook.