Wikimedia Bugzilla is closed!

If you make a page documenting a special built-in property like Property:Has_type, then it shows up as an unused property in Special:UnusedProperties even when pages do use it.

Conversely, special properties don't appear in Special:Properties, no matter how many pages use them.

Ideally, special properties in special pages, queries, and  "Pages using the property “xyz”" lists would work exactly the same as regular properties, except that (as in the factbox) the special property's title would appear in italics with a tooltip "This property is a special property in this wiki".

An easier(?) workaround would be to exclude any special property from Special:UnusedProperties.