Newbie forum problems - negative number of new posts reported

I'm new and starting with 4.5rc

I have several forums set up as follows:

In Categories, there is a vocabulary named "Discussion Forums" of type "forum topic", hierarchy = "multiple", and "multiple select" is checked (I'm not sure if I understand these last two). I have added several terms to act as Forum Topics. When I click on the forum link (at top of default theme), everything looks good and there is a table with headings "forum", "topics", "posts", "last post".

At first, this all worked fine. I made a number or test posts and replies, and deleted posts.

I think the problem may have started when I began renaming, re-arranging, and DELETING categories that already had things assigned to them. However, at one point I did delete all forum postings and category terms, and started over, but the problem persists.

Here's what's happening.

When I post a new forum topic, it all seems to work fine. No errors, and the posted message renders fine after submitting. But if I click back on the forums link to go to the main forums page, there are still zeros for "topics", "posts", "last post", and under topics, there's a hyperlink labeled "-1 new". Clicking it, or the forum title, both of which would usually show me the posted topic, always show only empty forum pages (headers with no posts).

If I continue to post more topics, the negative numbers increase (i.e. "-2 new", "-3 new", etc.). The posted topics are never available, except if I browse the archives. There they all show up. So it seems they are being posted, just not tracked properly.

Help?