Invisible option besides announcements which makes topics invisible.

I did a search, but didn't find anything useful, maybe because I couldn't think of any good term to search for. If the solution to this can be found easily and I'm just to blind for it, I'll excuse in advance.

When I edit a topic and want to sticky it or make it appear as announcement, I have a fourth option /besides normal, sticky, announcement) that I can check. This option is not named, ie. it's only the circle for the check. If I check it and save, the topic does not appear in the list of topics, however when I access the Moderator Control Panel, it's shown. What is this option for, how do I edit it, or how can I remove it?

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