ArgumentOutOfRangeException when using Union/UnionAll #3669

using LinqToDB;
using LinqToDB.Data;
using LinqToDB.DataProvider.Oracle;
using System;
using System.Collections;
using System.Collections.Generic;
using System.Data;
using System.Linq;
using System.Threading.Tasks;

namespace LinqToDBTest
{
    public class MyModel
    {
        public string ID { get; set; }
        public string COLA { get; set; }
    }

    internal class Program
    {
        static async Task Main(string[] args)
        {
            try
            {
                using (var conn = new DataConnection(ProviderName.MySqlConnector, ""))
                {
                    var q1 = from x in conn.GetTable<MyModel>()
                             where x.ID == "aaa"
                             select new
                             {
                                 x.ID,
                                 COLA = "A",
                                 OK = x.COLA == "123" ? "Y" : "N",
                             };
                    var q2 = from x in conn.GetTable<MyModel>()
                             where x.ID == "bbb"
                             select new
                             {
                                 x.ID,
                                 x.COLA,
                                 OK = "N"
                             };
                    //var query = q1.UnionAll(q2);
                    var query = q1.Union(q2);
                    var q3 = from x in query
                             from y in conn.GetTable<MyModel>().LeftJoin(t => t.ID == x.ID)
                             where x.ID == "ccc"
                             select new
                             {
                                 x.ID,
                                 x.OK,
                                 COLA = x.COLA == "ddd" ? y.COLA : x.COLA,
                             };
                    var list = await q3.ToListAsync();
                    Console.WriteLine(list.Count);
                }
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex);
            }
        }

    }
}