Caz's trick is to go back to one of your non-appearing posts, which you have to find by cycling through the post ids, since post history is deactivated in the profiles, and edit it. That somehow flushes the cache.

No need to go back to a non-appearing posts. It works on ANY comments from the same thread. You will need to find back your non-appearing post only if it is too late to edit one of your comment from the particular thread.

I guess the cache file system handle the event "edit" and not "post". Or order the thread by the last edit rather than the last post. Anyway, it is just a matter of a couple of minute to fix that feature.