Why aren't my taxonomy terms rendering?

This is driving me insane. I am calling

print render ($content['field_tags']);

in my node--type.tpl.php file, but nothing is rendering. I am successfully rendering all fields except my taxonomy fields using this call, and searching the web shows that this is indeed the right call. Nothing is being output. It's not a CSS problem, because the rendered page source shows nothing at all. I've checked countless times for typos, and I know the there are term ids associated with the node. I can see them when I do print_r($content);

Am I missing something obvious here? I am using a Zen subtheme if that matters.