When "custom" title is provided, both page-name-as-title value and Page_Title custom value are displayed.

1. Go to http://docs.webplatform.org/wiki/beginners

Note that the top section headers are:

beginners

Web development for beginners

2. Select "edit source" to confirm there is a custom value:

Note that the custom value is provided:

{{Page_Title|Web development for beginners}}

Expected (per http://docs.webplatform.org/wiki/Template:Page_Title):

"If title is not provided, it will default to showing the last part of the URL."

Actual: last part of the URL AND the custom page title value are displayed.