DataBase schema generation problem

I have created small sample to explain my problem. Model contains abstract entity User (who has two descendants Seller and Driver) , entity Marekt (who aggregates Sellers) and entity Car ( who aggregates Drivers). For User inheritance I use SingleTableInheritance. See picture of model in attach.
When LightSpeed model disigner generates DataBase schema then table User looks like:

CREATE TABLE [User] 

(

Id INT IDENTITY NOT NULL PRIMARY KEY ,
[Name] NVARCHAR(MAX) NOT NULL DEFAULT '',
[UserRole] INT NOT NULL DEFAULT 0,
[MarketId] INT NOT NULL DEFAULT 0,
[CarId] INT NOT NULL DEFAULT 0,

FOREIGN KEY (MarketId) REFERENCES [Market](Id),
FOREIGN KEY (CarId) REFERENCES [Car](Id)

);

The problem if I create Seller then I get SqlException:
The INSERT statement conflicted with the FOREIGN KEY constraint "FK__User__CarId__5AB9788F".

But Seller don't depend on Car!

What should I do in mine model that model Disigner can generate correct DataBase scheme?

You should make the Car association nullable -- select the Car -> Driver arrow, go to the Properties window and set Is Nullable to true.  This will cause LightSpeed to generate a nullable foreign key field which will allow you to insert Sellers who have no CarId.

In my case Car and Market are aggregates of Driver and Seller respectively. If I make Car association and Market association nullable then i can't remove Driver and Seller in my code like Market.Sellers.Remove( badSeller ) or Car.Driver.Remove( oldDriver ).

In my sample if I make by hand in DataBase fields CarId and MarketId nullable then all work fine.

My opinion if we use single table inheritance then the mandatory fields of this table are properties of base entity. The properties of descendants must be correlate to nullable fields. Why LightSpeed doesn't make fields of descendants as nullable?

In current nightly builds, it does.  You can get the latest nightly from http://www.mindscapehq.com/downloads/

Thanks a lot. You rock!