This is a normal Topic History page:
https://www.mediawiki.org/w/index.php?title=Topic:S7ry1w85n5o2axy9&action=history

This link is just an individual Post's history.
https://www.mediawiki.org/w/index.php?title=Topic:S7ry1w85n5o2axy9&action=history&topic_postId=s7s0gnlsjnk3d7go

It looks the same, and is therefore confusing to anyone who is wondering why the rest of the topic history isn't showing up.

Note: Post history pages are linked to from the "hist" link in our Contributions page (for content-changing-edits), but nowhere else?
https://www.mediawiki.org/w/index.php?title=Special:Contributions/Quiddity_(WMF)&offset=20141211193343&limit=2&target=Quiddity+(WMF)
(We should probably re-examine this, separately)