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When I set announce when creating a discussion it seems that when I choose both "in category" and "in category and recent discussions" the discussion is pinned in recent discussions.
When I chose to edit the discussion the same behavior applies, as long as I have chosen one of the two options to announce it will always be pinned in "recent discussions".
However, changing announcement behavior via the context menu from the cog-wheel It works to set it to only be shown in the category. In fact, in this menu it shows up as "in category and recent discussion", even if it was set to and still shows as "in category" when editing och creating a new one.