Unbuffered QueryAsnyc multi-mapping throws an InvalidOperationException

using (var conn = new SqlConnection(appToken.ConnectionString))
{
    conn.Open();
    var ret = conn.Query("select a='dog',b=3", (string a, int b) => a + b, splitOn: "b", buffered: false);
    Console.WriteLine(string.Join("", ret));
    ret = conn.QueryAsync("select a='dog',b=3", (string a, int b) => a + b, splitOn: "b", buffered: false).Result;
    Console.WriteLine(string.Join("", ret));
}

The call to Query returns dog3, the QueryAsync throws the following exception:

System.InvalidOperationException was unhandled
  HResult=-2146233079
  Message=Invalid attempt to call FieldCount when reader is closed.
  Source=System.Data
  StackTrace:
       at System.Data.SqlClient.SqlDataReader.get_FieldCount()
       at Dapper.SqlMapper.GetColumnHash(IDataReader reader, Int32 startBound, Int32 length)
       at Dapper.SqlMapper.<MultiMapImpl>d__140`8.MoveNext()
       at System.String.Join(String separator, IEnumerable`1 values)
       at Program.Main(String[] args) in 

The store procedure I am calling takes a while to execute and I'd rather let it be called async before I start streaming data out of the query.

Start with the Query and QueryAsync entry points and reproduce the shown multi-mapping call against the SQL query with buffered set to false. Compare the synchronous and asynchronous enumeration paths and verify that the reader remains usable while results are streamed. Done means QueryAsync produces dog3 without the closed-reader InvalidOperationException.