I see that you added
// Use the columns of the "Open" queue as a default template
if ($use_template && ($template = CustomQueue::lookup(1)))
return $template->getColumns();
To the code, but when I tried it I get the same, default search columns. I tried putting that snippet at the very start of the function (under function getColumns($use_template=false) {) to try to force it to return the results as early as possible, but no results. I tried just a return of $template->getColumns();, but that just resulted in an error breaking the page.
I'm also currently running version 1.15.2. Any help would be really appreciated.
Edit: I've also gone through the standard columns portion a few lines down. I added a required field under Contact Information called "practices." I tried calling it using various versions of "primary" => 'cdata__practices', as well as user_practices, and just about everything else I could think of.
Thanks so much!