I just noticed that the list of subscribed threads in MyFlyerTalk seemed to not include several threads I'd started.

It turns out that when I post a new thread, setting the dropdown to Instant Email Notification doesn't do anything. But if I later go to the thread, and pick Subscribe to This THread from the Thread Tools menu, it does add the subscription.

I don't know if this is related to my never getting emails about new posts to my threads, but it's definitely a bug.