WebAPI + EF5, Entity framework does not recover from a DBUpdateException and requires a full restart of the service - asp.net-web-api

Question

I have two table in my database. Table USER and table USER_ADDRESSES
Table USER has UserID , UserName , HumanName
Table USER_ADDRESSES has UserAddresseID, UserID, Address
The two tables are related through the UserID foreign key.
I am working code first. The POCOs are as one would expect I guess:
Public class User
{
Public guid UserID {get;set;}
Public string UserName {get;set;}
Public string HumanName {get;set;}
}
Public class UserAddress
{
Public guid UserAddressID {get;set;}
Public guid UserID {get;set;}
Public string Address {get;set;}
Public virtual User User {get;set;}
}
If I POST a user, it flows through EF and into the physical database - cool
If I POST a UserAddress with the UserID foreign key properly assigned as the UserID of the above user, the userAddress flows through EF into the physical database - perfect.
Now as I am learning this subject, I like to test scenarios that I know will cause errors… Understanding how something fails often leads to greater understanding (IMHO).
To this end, I repeat the above steps.POST a user, then POST an Address but this time with an empty GUID in the Address.UserID property, something I know will cause SQL server to error on,this time EF gets an error back from the DB and surfaces that error in my controller class as a DbUpdateException, which I then act upon to send back a BadRequest ErrorResponse, this would be fine except now I can post nothing to the DB, If I subsequently try to post new Users EF throws a DbUpdateException on every POST. The only way out of this condition is to Stop debugging the WebAPI project, kill IISExpress and restart everything.
My suspicion is that it is something to do with the tracked entities in dbset.Local it appears this collection is happy to store entities which violate database constraints, and even after the DB has thrown an error EF does not remove the faulted entity from its cache, and I guess that every time I call DataContext.SaveChanges(), EF keeps trying to submit the Faulty address entity that it has in it's bdset.Local property and thus prevents me from submitting anything further to the DB until the whole project is restarted and the various dbset.Local collections are flushed.
Ok I understand that, In my controller class I can prevent some of these issues by evaluating the various properties of the object before submitting them to my repository/UnitOfWork and thus prevent them from getting into dbset.Local in the first place, perhaps there is some decoration I can add to my POCOs such that ModelState.IsValid returns false if UserID == Guid.Empty in the UserAddress Entity??? . But surely EF should be able to recover from DB originated errors, such that if an INSERT statement fails when run against SQL server, EF should remove the faulting Entity from its Local cache of tracked objects. Thus preventing the whole system from requiring a complete restart. The upshot of this is that if I had unique constraints on other non key fields, before I attempt to submit an entity I will have to query the DB to ensure that there are no records in the DB which would result in a DBUdateException from being thrown, that approach seems inefficient to me. I would rather take the error and throw it back to the client for them to consider.
Now perhaps it's my responsibility that on the occurrence of a DbUpdateException to do something to remove the faulted entity from the dbset.Local collection or similar. If that's the case how should I go about this?
As I have been writing this I am left wondering: Should EF not be able to recover from DBUdateExceptions in and of its self!? Without the need for an IIS restart. Or should I build my DB with no constraints what so ever and allow clients to put any old rubbish in there. It's my believe that EF Entity tracking should honour db constraints and prevent faulted entities from getting into the dbset in the first place.
Please guide me on the correct way to recover from a DBUpdateException?