Combined_fields + dfs_query_then_fetch causes error

Using combined_fields query with dfs_query_then_fetch causes "docCount must not exceed maxDoc" error if the request goes to multiple shards. Quick example to reproduce the issue
(Elasticsearch v7.13.4, v7.15.0)

PUT /my-index
{
  "settings": {
    "index": {
      "number_of_shards": 2 
    }
  }
}

POST /my-index/_doc
{
  "name": "item 1",
  "description": "description 1"
}
POST /my-index/_doc
{
  "name": "item 2",
  "description": "description 2"
}

POST /my-index/_search?search_type=dfs_query_then_fetch
{
  "query": {
    "combined_fields": {
      "fields": [
        "name", "description"
      ],
      "query": "item"
    }
  }
}

Response:

{
  "error" : {
    "root_cause" : [
      {
        "type" : "illegal_argument_exception",
        "reason" : "docCount must not exceed maxDoc, docCount: 2, maxDoc: 1"
      }
    ],
    "type" : "search_phase_execution_exception",
    "reason" : "all shards failed",
    "phase" : "dfs_query",
    "grouped" : true,
    "failed_shards" : [
      {
        "shard" : 0,
        "index" : "my-index",
        "node" : "iieOmNBaRkaOGjyQCQw6Bg",
        "reason" : {
          "type" : "illegal_argument_exception",
          "reason" : "docCount must not exceed maxDoc, docCount: 2, maxDoc: 1"
        }
      }
    ],
    "caused_by" : {
      "type" : "illegal_argument_exception",
      "reason" : "docCount must not exceed maxDoc, docCount: 2, maxDoc: 1",
      "caused_by" : {
        "type" : "illegal_argument_exception",
        "reason" : "docCount must not exceed maxDoc, docCount: 2, maxDoc: 1"
      }
    }
  },
  "status" : 400
}

Thanks for catching this @cyradin! Could you please file a GitHub issue in our repo (GitHub - elastic/elasticsearch: Free and Open, Distributed, RESTful Search Engine) so we can track and address the bug?