If you have a page structure that happens to follow exactly the structure expected by inherited nodes, you run into ugly issues.
To reproduce with the stk demo:

• create a page under demo-project/about called promos
• view demo-project/about; there should be a FreeMarker error on the right side of the page, where the promos are supposed to be displayed.

The same can happen if

• using jcr browser, remove demo-project/about/extras.
• create a page under demo-project/about called extras, then a subpage to that called extras1.
• view demo-project/about.

(less likely, of course...)