I found a good work around for anyone else that might run into a similar problem. For some reason adding the message-list to a custom component breaks it for me, so I added my logic to an override component for the message-list like so:
<#assign activeTab = http.request.parameters.name.get("tab", "all") />
<#if activeTab == "all">
<@delegate/>
</#if>
And left the message-list added directly to my custom Forum Page quilt. <@delegate> doesn't break the message-list.
One problem with this approach is that I am only adding filter tabs to a custom Forum Page that we won't be using for every forum. By overriding the message-list I will also be affecting the default forum page. However, since the default behavior is to show the message list if there is no "?tab=" parameter in the URL this shouldn't be an issue. It will just behave normally on the default forum page.
