Question Trick to configuring RECENT DISCUSSIONS?

Is there a trick to how RECENT DISCUSSIONS will show posts in a forum?

Should it show ALL of the most recent discussions?

Or...

Does it only show recent discussions within some time frame?

On my test site, J1.5.10, K1.09 I have one forum group with 3 forums within. If they are all set to REGISTERED in the config I see only the new posts I have not yet read. After I read them, and then click on recent discussions again it will show NO POSTS. I cleared the site cache and checked again after setting the permissions to "ALL REGISTERED" and then I see the post I made 2 hours ago with 0 replies and it is listed as READ.

I don't understand and I may be over complicating something, but after searching ten pages deep into "RECENT DISCUSSIONS" the only thing I grasp is that maybe something should be in the field "Show Category" under Recent Post Settings on the config screen. Right now its BLANK.

If I had my choice I would prefer that it simply list ALL recent discussions, in order they were posted in whether a user has them as new, or not. I believe that’s what it is supposed to do?

What have I missed here?

I think the default "view" for the Recent Discussions tab is to show topics that were updated in the last month, as illustrated here

Also, if you are not logged-in and you're viewing the Recent Discussions tab, you won't see topics that were updated in any "registered users only" categories.

I hope that helps.