I can't exactly pinpoint what was the cause, but when I had Devel Themer turned on, some of the HTML got broken. The render HTML code looks like this:
<span class="thmr_call" id="thmr_82">
id="node-supplier_2-74" class="node supplier_2 published not-promoted not-sticky full-view self-posted author-superadmin odd clear-block"</span>
This is nothing critical (Themer is not meant for user access anyway), but it's an eye sore when we are trying to theme the site.