Stream schema does not seem to be respected in produced records

I might be misunderstanding how the schema definition works for a stream, but this bothers me.
With the following schema (from issue_comments in 71b07b7ba4cdfc13f7a2c651252d163206e5c56f):

    schema = th.PropertiesList(
        th.Property("id", th.IntegerType),
        th.Property("node_id", th.StringType),
        th.Property("repo", th.StringType),
        th.Property("org", th.StringType),
        th.Property("issue_url", th.IntegerType),
        th.Property("updated_at", th.DateTimeType),
        th.Property("created_at", th.DateTimeType),
        th.Property("author_association", th.StringType),
        th.Property("body", th.StringType),
        th.Property(
            "user",
            th.ObjectType(
                th.Property("login", th.StringType),
                th.Property("id", th.IntegerType),
                th.Property("node_id", th.StringType),
                th.Property("avatar_url", th.StringType),
                th.Property("gravatar_id", th.StringType),
                th.Property("html_url", th.StringType),
                th.Property("type", th.StringType),
                th.Property("site_admin", th.BooleanType),
            ),
        ),
    ).to_dict()

I am seeing the following records:

{
  "type": "RECORD",
  "stream": "issue_comments",
  "record": {
    "issue_url": "https://api.github.com/repos/singer-io/tap-facebook/issues/157",
    "id": 895733451,
    "node_id": "IC_kwDOBRvyIM41Y87L",
    "user": {
      "login": "lscottallen004",
      "id": 83940128,
      "node_id": "MDQ6VXNlcjgzOTQwMTI4",
      "avatar_url": "https://avatars.githubusercontent.com/u/83940128?v=4",
      "gravatar_id": "",
      "url": "https://api.github.com/users/lscottallen004",
      "html_url": "https://github.com/lscottallen004",
      "followers_url": "https://api.github.com/users/lscottallen004/followers",
      "following_url": "https://api.github.com/users/lscottallen004/following{/other_user}",
      "gists_url": "https://api.github.com/users/lscottallen004/gists{/gist_id}",
      "starred_url": "https://api.github.com/users/lscottallen004/starred{/owner}{/repo}",
      "subscriptions_url": "https://api.github.com/users/lscottallen004/subscriptions",
      "organizations_url": "https://api.github.com/users/lscottallen004/orgs",
      "repos_url": "https://api.github.com/users/lscottallen004/repos",
      "events_url": "https://api.github.com/users/lscottallen004/events{/privacy}",
      "received_events_url": "https://api.github.com/users/lscottallen004/received_events",
      "type": "User",
      "site_admin": false
    },
    "created_at": "2021-08-10T05:09:01Z",
    "updated_at": "2021-08-10T05:09:01Z",
    "author_association": "NONE",
    "body": "> \n\n- > > > > > > ~~> >~~~~~~~~> @iterati _@iterati _@iterati _[]()[]()_@hz-lschick ____>~~ []",
    "org": "singer-io",
    "repo": "tap-facebook"
  },
  "time_extracted": "2021-09-10T23:07:19.736119Z"
}

A number of the nested *_url fields are present in the record, although they are excluded from the schema definition. It looks like a call to https://gitlab.com/meltano/sdk/-/blob/main/singer_sdk/helpers/_singer.py#L23 from pop_deselected_record_properties causes the field to be included because user is included, and somehow the details of the nested object do not appear in the selection mask.

I suspect this is a bug in the sdk, but I might have misunderstood how the code is supposed to work 🤔

Start with pop_deselected_record_properties in singer_sdk/helpers/_singer.py and reproduce the issue using the issue_comments schema shown here. Check how the nested user selection mask is built; done when fields such as the nested *_url properties that are absent from the schema are omitted from produced records.