Test case for bug? Tested on 3.0.3751-Unstable and 3.0.3690

IsInAsyncErrorInRavenDb.cs

using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Raven.Client;
using Raven.Client.Embedded;
using Raven.Client.Indexes;
using Raven.Client.Linq;
using Raven.Tests.Helpers;
using Xunit;

namespace ClassLibrary1
{
    public class IsInTriggersSyncFromAsync : RavenTestBase
    {
        private readonly EmbeddableDocumentStore _store;

        public IsInTriggersSyncFromAsync()
        {
            _store = NewDocumentStore();
            new Index().Execute(_store);
            using (var session = _store.OpenSession())
            {
                session.Store(new Entity
                {
                    Id = "solo",
                    Tokens = new List<string>
                    {
                        "ABC",
                        "DEF"
                    }
                });
                 session.SaveChanges();
            }
        }

        [Fact]
        public async Task IsInTriggersSyncFromAsyncException()
        {
            using (var session = _store.OpenAsyncSession())
            {
                var queryToken = "ABC";
                var entity = await session.Query<Entity, Index>()
                    .Customize(q => q.WaitForNonStaleResults())
                    .Where(e => e.Id == "solo" && queryToken.In(e.Tokens))
                    .FirstOrDefaultAsync();
                Assert.NotNull(entity);
                Assert.Equal("solo", entity.Id);
            }
        }
        [Fact]
        public async Task WithoutIsInItWorks()
        {
            using (var session = _store.OpenAsyncSession())
            {
                var queryToken = "ABC";
                var entity = await session.Query<Entity, Index>()
                    .Customize(q => q.WaitForNonStaleResults())
                    .Where(e => e.Id == "solo")
                    .FirstOrDefaultAsync();
                Assert.NotNull(entity);
                Assert.Equal("solo", entity.Id);
            }
        }
    }

    internal class Entity
    {
        public string Id { get; set; }
        public List<string> Tokens { get; set; }
    }

    internal class Index : AbstractIndexCreationTask<Entity>
    {
        public Index()
        {
            Map = entities => from entity in entities
                select new
                {
                    entity.Tokens
                };
        }
    }
}