Shouldn't happen on this site, since it uses timestamps to paginate instead of just pages, meaning you'll see 10 posts after the last post on that page instead of the 10 posts that come after the first 10 posts on that page.
i think i've seen this happen in tag search too, but never on the main dashboard. It hasn't bothered me too much but it might be a problem if it's a REALLY active tag.
Cirassa
As far as i see, currently when viewing dash, tags or users, you can "go to next page" rather than scroll infinitelly, like on facebook, tumblr, twitter (or X idk). But then if that place is really active, you end up seeing old posts on new page. For example, viewing lets say #art, you scroll down, and see last post, you go to next page, and that post is suddenly at top of it, beacuse someone posted something new in #art