This happens when you close or open topics; it can happen when you assign topics and in various other conditions.
Over the years, we have heard many complaints from people who simply do not want to be notified about this administrivia. This is particularly noticeable when admins bulk close topics or can come as a surprise when topics are auto-closed due to timers.
We are partway through rolling out a change that will exclude all small actions from your Watched and Tracked lists.
We will not be making this optional. We track two counters on the topics table so we know what the last post is on a topic; we do not want to inflate that to four counters.
Let us know what you think and if you feel like it will impact your forums.
I noticed that the “closed” small action posts on topics here on Meta now always appear as unread. The “last visit” line is always above, not only once and the next time I visit the topic there is no line because everything is read
