CMS by Drupal
As of now, the site forum seems to be functional, and should work normally.
To review, the problem was that new forum topics were appearing indicating "this topic has been moved", which wasn't terribly useful. I should leave at least some breadcrumb trail indicating how I accomplished this little hack.
First, I spent a long time meditating over the internals of forum and other modules, and reviewing to see if one of my Drupal hacks was responsible for the problem. Martin Hoch helped me at one point, but we were fairly lost.
Then tonight I managed to find the right Google query to find a report of others with the same bug (#40394, #54493). The root cause seemed to be that the forum module gets very confused if the vocabulary being used for forum names is allowed to have more than one simultaneous selection. (To review, a Drupal news posting is a "forum topic" which may have comments. The topic sits in a "forum". The forum may have a "container". The forum and container names are selected from the "forum vocabulary" and "container vocabulary", which are in the "categories" list.)
At that point it was a simple matter of creating a new forum vocabulary, making sure it was set up properly, then doing a bunch of database queries to make everything point at the new vocabulary. This was a lot harder than I thought it would be; partly because I tried a hack to clone the existing forum vocabulary that didn't work. I think I like the new one better anyhow, though.
Let me know if there are still issues.