I don't run Xenforo on a live community yet, so the most I get to do is play around with it on localhost but a moment ago I edited my username through the admin panel, and it seems to have updated it all around the site apart from on the forumhome last post and the forum view last post section.
I first changed my username from 'S' to 'Storm', it updated everywhere apart from the last post sections. Here's a screenshot, looks at all the 'usernames'. They're inconsistent, seems like a bug to me. Here's a screenshot: