First the good news: Everything works.
Now, the odd part. I have some lines that I like to have in my .htaccess to help with some urls that changed a while back. I noticed this morning that my rewrite rules were once again not firing, so I added 'em back in, tested and all was fine.
12 hours later (now) I glance at the logs and see, again, that my rules aren't firing. I edit .htaccess to see if I had a typo and my rules are gone! Everything else is the same, just minus the 3 lines I added. Fortunately, this time I had saved a backup so was able to quickly restore it.
But what causes this? I was in the admin area today, but I didn't go anywhere near the Permalinks section. I wrote a new post and I added a new page. Would one of those force a "routine" .htaccess change by WP?