One of my hosts (the better performer) does not show up in my User Host List. However, when I click the Host List in My BAM Menu I can see both hosts.

This link shows only one host active when I do indeed have two hosts:
http://boincstats.com/stats/boinc_host_stats.php?pr=bo&st=0&userid=b9579faec1fed89d2e7f0b1f221f3c19

This link shows both hosts as I would expect (I know you cannot see this, but this is the Host List link I am using).
http://boincstats.com/bam/host_list.php

This is the host that is missing:
http://boincstats.com/stats/boinc_host_graph.php?pr=bo&id=6d27d23fb3e43b0d88f9fdd0cf49d191

Thanks for your help in figuring out what bug or problem this might be!

I should also mention that these are both Linux hosts and that only one of the two Linux hosts is properly reporting in the hosts list under my detailed stats.

Strange. Now it appears...

Sometimes you have to be patient. The host needs credit first, then it has to be exported by the project to XML files, and then BOINCstats has to import it and do a stats update. It can take a few days before all this has happened.