Pretty much as the subject, when viewing the topic lists you would get a preview of the pinned topics but after refresh these previews would disappear. Following the recent site update this no longer happens.
This is indeed to correct behaviour. If you want to remove the preview (we call the the excerpt), you will need to unpin that topic.
Please note I am not an admin of this site.
This never used to happen, on the first load of the topic list view I would see the excerpt, if I refreshed the page the excerpts would disappear. No unpinning was done.