I have observed duplicates in the Usages section of the documentation.
You can very that in the WiX sample output you posted, the WiX.chm:
1. From the TOC navigate to the Simple Types in the http://schemas.microsoft.com/wix/2006/wi Namespace (second).
2. Click on the simple types, most including the first show duplication. The first looks like
Id (Icon) Id (Icon)
May be the only way to show the difference is to prepend the parent elements like...
(Icon) Package/Id (Icon)