Collection @id field is not unique.

While querying for items in the site, I ended up with duplicate @ids. I found out that apparently the global querystring endpoint is returned as the @id for Collections, instead of the url.
Here is the api query i tried. I sent a POST to http://localhost:8080/Plone2/@querystring-search with the following body:

{
    "query": [
        {
            "i": "path",
            "o": "plone.app.querystring.operation.string.relativePath",
            "v": "."
        },
        {
            "i": "portal_type",
            "o": "plone.app.querystring.operation.selection.any",
            "v": "Collection"
        }
    ],
    "fullobjects": 1
}

And this is the response I got:

{
  "@id": "http://localhost:8080/Plone2/@querystring-search",
  "items": [
    {
      "@components": {
        "actions": {
          "@id": "http://localhost:8080/Plone2/news/aggregator/@actions"
        },
        "breadcrumbs": {
          "@id": "http://localhost:8080/Plone2/news/aggregator/@breadcrumbs"
        },
        "navigation": {
          "@id": "http://localhost:8080/Plone2/news/aggregator/@navigation"
        },
        "types": {
          "@id": "http://localhost:8080/Plone2/news/aggregator/@types"
        },
        "workflow": {
          "@id": "http://localhost:8080/Plone2/news/aggregator/@workflow"
        }
      },
      "@id": "http://localhost:8080/Plone2/@querystring-search",
      "@type": "Collection",
      "UID": "5652964873654ed58c6989036c1d096c",
      "allow_discussion": false,
      "contributors": [],
      "created": "2020-01-10T11:46:26+00:00",
      "creators": [
        "admin"
      ],
      "customViewFields": [
        {
          "title": "Title",
          "token": "Title"
        },
        {
          "title": "Creator",
          "token": "Creator"
        },
        {
          "title": "Type",
          "token": "Type"
        },
        {
          "title": "ModificationDate",
          "token": "ModificationDate"
        }
      ],
      "description": "Notizie del sito",
      "effective": null,
      "exclude_from_nav": false,
      "expires": null,
      "id": "aggregator",
      "is_folderish": false,
      "item_count": 30,
      "items": [],
      "items_total": 0,
      "language": "",
      "layout": "summary_view",
      "limit": 1000,
      "modified": "2020-01-10T11:46:26+00:00",
      "parent": {
        "@id": "http://localhost:8080/Plone2/news",
        "@type": "Folder",
        "description": "Notizie del sito",
        "review_state": "published",
        "title": "Notizie"
      },
      "query": [
        {
          "i": "portal_type",
          "o": "plone.app.querystring.operation.selection.any",
          "v": [
            "News Item"
          ]
        },
        {
          "i": "review_state",
          "o": "plone.app.querystring.operation.selection.any",
          "v": [
            "published"
          ]
        }
      ],
      "relatedItems": [],
      "review_state": "published",
      "rights": "",
      "sort_on": "effective",
      "sort_reversed": true,
      "subjects": [],
      "text": null,
      "title": "Notizie",
      "version": "current"
    },
    {
      "@components": {
        "actions": {
          "@id": "http://localhost:8080/Plone2/events/aggregator/@actions"
        },
        "breadcrumbs": {
          "@id": "http://localhost:8080/Plone2/events/aggregator/@breadcrumbs"
        },
        "navigation": {
          "@id": "http://localhost:8080/Plone2/events/aggregator/@navigation"
        },
        "types": {
          "@id": "http://localhost:8080/Plone2/events/aggregator/@types"
        },
        "workflow": {
          "@id": "http://localhost:8080/Plone2/events/aggregator/@workflow"
        }
      },
      "@id": "http://localhost:8080/Plone2/@querystring-search",
      "@type": "Collection",
      "UID": "743e2066df7044b88bee59c491d796cf",
      "allow_discussion": false,
      "contributors": [],
      "created": "2020-01-10T11:46:27+00:00",
      "creators": [
        "admin"
      ],
      "customViewFields": [
        {
          "title": "Title",
          "token": "Title"
        },
        {
          "title": "Creator",
          "token": "Creator"
        },
        {
          "title": "Type",
          "token": "Type"
        },
        {
          "title": "ModificationDate",
          "token": "ModificationDate"
        }
      ],
      "description": "Eventi del sito",
      "effective": null,
      "exclude_from_nav": false,
      "expires": null,
      "id": "aggregator",
      "is_folderish": false,
      "item_count": 30,
      "items": [],
      "items_total": 0,
      "language": "",
      "layout": "event_listing",
      "limit": 1000,
      "modified": "2020-01-10T11:46:27+00:00",
      "parent": {
        "@id": "http://localhost:8080/Plone2/events",
        "@type": "Folder",
        "description": "Eventi del sito",
        "review_state": "published",
        "title": "Eventi"
      },
      "query": [
        {
          "i": "portal_type",
          "o": "plone.app.querystring.operation.selection.any",
          "v": [
            "Event"
          ]
        },
        {
          "i": "review_state",
          "o": "plone.app.querystring.operation.selection.any",
          "v": [
            "published"
          ]
        }
      ],
      "relatedItems": [],
      "review_state": "published",
      "rights": "",
      "sort_on": "start",
      "sort_reversed": true,
      "subjects": [],
      "text": null,
      "title": "Eventi",
      "version": "current"
    }
  ],
  "items_total": 2
}

Both results have the same @id. If I remove fullobjects the response contains the actual collection url in the @id field.

This is a fresh Plone site with just restapi installed, running on the latest Plone 5.2.1-pending with plone.restapi 6.1.0.

Start by reproducing the POST to the @querystring-search endpoint with the issue's query and compare responses with and without fullobjects. Trace how Collection results receive their @id values; done means fullobjects responses use each collection's actual URL rather than the shared query endpoint, with distinct @id values for both results.