Weird linq2sql/let bugs?

Question

Can someone explaing why existence of the following linq query...

(from e in db.Clients
        let
         log = (from f in db.CreditsafeLogs where f.Vat.Equals(e.VAT) orderby f.Sent descending select f).FirstOrDefault()
        where
         e.DeleteFlag.Equals("n") &&
         e.Active == true &&
         log != null &&
         log.Approved == false
        select e.Id)

compiles, but in runtime breaks the application (even though it's never called), while it's equivalent

Clients
   .Select (
      e => 
         new  
         {
            e = e, 
            log = CreditsafeLogs
               .Where (f => f.Vat.Equals (e.VAT))
               .OrderByDescending (f => f.Sent)
               .FirstOrDefault ()
         }
   )
   .Where (
      temp0 => 
            (((temp0.e.DeleteFlag.Equals ("n") && (temp0.e.Active == (Boolean?)True)) && 
                  (temp0.log != null)
               ) && 
               (temp0.log.Approved == False)
            )
   )
   .Select (temp0 => temp0.e.Id)

Works fine??

Answer 1

Since we have no way of reproducing it, can you define "breaks the application"? Can you cite the error message please? For info, I have occasionally seen the expression compiler make dubious decisions about nullability - for more see here. This might be related, but impossible to say without the error message.