First off, I know this resource is in beta. I'm not sure if this is an issue or not, or if you are aware of it.
When I do a search for DiagnosticReport I get back 2. The 2nd one has the result property set with a list of observations.
The issue is, when i do an Observation search (with category = laboratory), the observations listed in the DiagnosticReport do not show up. I took one of the observation id's from the DiagnosticReport and did a direct query on that id and it came back, and it did reference the correct patient. So I'm not sure what's going on.