Entity Framework 4 With Ctp5 And Dirty Generated Sql

I have a problem with strange generate sql in ef4 ctp5. I have simple model with mapping :

[Table("post_auction")]
public class PostAuction
{
[Key,Column(Name="Id"),DatabaseGenerated(System.ComponentModel.DataAnnotations.DatabaseGenerationOption.Identity)]
public int Id { get; set; }
[Column(Name = "Number")]
public int Number { get; set; }
[Column(Name = "Label")]
public string Label { get; set; }
[Column(Name = "Description")]
public string Description { get; set; }
[Column(Name = "CategoryId")]
public int PostAuctionCategoryId { get; set; }
[Column(Name = "PriceCZK")]
public int PriceCZK { get; set; }
[NotMapped]
public bool IsAuctionPhotoExitst
{
get
{
if (File.Exists(HttpContext.Current.Server.MapPath("~/Public/Images/Posts/Thumbs/small_" + this.Number + ".jpg")))
return true;
return false;
}
}
}

and my linq query is :...............