Simple example - two templates:
<script type="text/x-jsrender" id="tpl-test1">
<div>{{include tmpl="tpl-test2" /}}</div>
</script>
<script type="text/x-jsrender" id="tpl-test2">
<div>Hello World</div>
</script>
If I render tpl-test1, it displays "tpl-test2" in the browser instead of Hello World. If I render tpl-test2, it renders Hello World just fine.
What gives?
Boris, himself, answered my question. The {{include}} needs to specify a selector.
Thought I'd post this in case anyone else experiences a similar brain fart. ;-)