Properties can be live or dead. Live properties are properties that are known to the WebDAV server (in this case, HCP). The server can respond to changes you make to these properties and can also dynamically modify their values.
Dead properties are properties that are not known to the WebDAV server. The server stores and retrieves these properties but does not do anything else with them. Dead properties can be in any XML namespace.
A PROPFIND request for all properties returns both live and dead properties. However, when responding to such a request, the server may omit live properties whose values are expensive to calculate.
In response to a PROPFIND request for all properties, HCP may omit some standard WebDAV properties but always includes all properties defined in the HCP XML namespace.