Something is wacky with this thread...I have the checkbox to "show unapproved nodes" set, but I still can't see the last three posts,

Everyone can see unapproved nodes. That setting simply controls whether they're shown in Seekers of Perl Wisdom and similar.

Perhaps what you want is to increase the reply depths (see the bottom of User Settings). If that's the problem, you can also see the "missing" nodes by viewing a less distant ancestor than the root node of the thread.