I have used the Help, report bug to submit a few items, but I don't see them on http://www.kdenlive.org/mantis (I clicked arround looking for "newest" and such.

I am wondering if it works before I bother using it for more.

Are they held up for moderation?

No defects on mantis are not held for moderation.

Go to http://www.kdenlive.org/mantis/view_all_bug_page.php - select advanced filters and filter by reporter and choose your user name.
Look at the status filtering too - make sure it is "any".