Why does EF generate this sql when querying reference property

Question

When using the AdventureWorks database and issuing this query:

   AdventureWorksEntities entities = new AdventureWorksEntities();
   entities.Contacts.Where(x => x.FirstName == "A" 
                               || x.FirstName == "B" 
                               || x.FirstName == "C")
                     .ToList();

Will be translated to this sql, which is the best it can:

//ommited for brevity
FROM [Person].[Contact] AS [Extent1]
WHERE [Extent1].[FirstName] IN (N'A',N'B',N'C')

However when I issue this query:

entities.Employee.Where(x => x.Contact.FirstName == "A" 
                             || x.Contact.FirstName == "B" 
                             || x.Contact.FirstName == "C")
                .ToList();

I get this SQL:

//ommited for brevity
FROM   [HumanResources].[Employee] AS [Extent1]
INNER JOIN [Person].[Contact] AS [Extent2] ON [Extent1].[ContactID] = [Extent2].[ContactID]
LEFT OUTER JOIN [Person].[Contact] AS [Extent3] ON [Extent1].[ContactID] = [Extent3].[ContactID]
WHERE [Extent2].[FirstName] = N'A' OR [Extent3].[FirstName] IN (N'B',N'C')

Why am I getting an inner and outer join and is EF splitting the where across both of them?

Of Note using contains creates the same SQL:

var names = new List<string>{"A", "B", "C"};
entities.Employee.Where(x => names.Contains(x.Contact.FirstName)).ToList();

EDIT: So it appears to be a EF bug, I've accepted the answer which provided a work around

EDIT: Opened connect issue, it's located here

Answer 1

Write a Stored Procedure which accepts a TVP as input parameter and let EF materialize the results from the SP :)