Do I understand things correctly that when a pinned topic only has a single post, the topic gets unpinned as soon as that post is displayed for the user? Or only after it has been displayed for a certain amount of time?
I think it would be good if the automatic unpinning would only be triggered if a topic has been viewed for a certain amount of time. Reason: if you pin a topic, the idea is to make sure that people read it. If it is only one post (perhaps because it is a closed announcement) and people only briefly look at it, you might want to keep it pinned for them until they take a closer look.