sorting Appointment on location sorts on first elem in participant table instead of location

[karsiwek-kainos]

select fhir_search('{"resourceType":"Appointment", "queryString":"_sort=location"}');

sorts data on first element in "participant" and it should look for location type actor.

example:
having appointments:

{  
    "resourceType":"Appointment",
    "id":"1",
    ...
    "participant":[  
        {  
            "actor":{  
                "reference":"Patient/2",
                "display":"Peter James Chalmers"
            },
            "required":"information-only",
            "status":"accepted"
        },
        {  
            "actor":{  
                "reference":"Location/2",
                "display":"location B"
            },
            "required":"required",
            "status":"accepted"
        },
  ...
    ]
}
{  
    "resourceType":"Appointment",
    "id":"2",
    ...
    "participant":[  
        {  
            "actor":{  
                "reference":"Patient/3",
                "display":"Peter James Chalmers"
            },
            "required":"information-only",
            "status":"accepted"
        },
        {  
            "actor":{  
                "reference":"Location/1",
                "display":"location A"
            },
            "required":"required",
            "status":"accepted"
        },
  ...
    ]
}
{  
    "resourceType":"Appointment",
    "id":"2",
    ...
    "participant":[  
        {  
            "actor":{  
                "reference":"Patient/1",
                "display":"Peter James Chalmers"
            },
            "required":"information-only",
            "status":"accepted"
        },
        {  
            "actor":{  
                "reference":"Location/3",
                "display":"location C"
            },
            "required":"required",
            "status":"accepted"
        },
  ...
    ]
}

query : select fhir_search('{"resourceType":"Appointment", "queryString":"_sort=location"}'); should return appointments in order 2,3,1 (id's), but returns 3,1,2.

it looks like it's sorting patients and not locations.