PLINQO many-to-many .Remove(...)

Why, in PLINQO, is the fo开发者_JAVA百科llowing valid;

parent.ManyToManyChildList.Add(child)
context.SubmitChanges();

But the following is not?

parent.ManyTomanyChildList.Remove(child)
context.SumbmitChanges();

Using Remove(), attempts to set the parent FK part of the many-to-many table's PK to null. Is the only way to delete the relationship using PLINQO via this?

context.ManyToManyEntity.DeleteOnSubmit(entity)
context.SubmitChanges();

Opening the .DBML (in the xml editor) and setting the foreign key association.DeleteOnNull="true' on the many-to-many table's parent-side of the foreign key fixed this.

<Table Name="dbo.ParentChild" Member="ParentChild">
    <Type Name="ParentChild">
      <Column Name="ParentId" Storage="_parentId" Type="System.Int32" DbType="int NOT NULL" IsPrimaryKey="true" CanBeNull="false" />
      <Column Name="ChildId" Storage="_childId" Type="System.Int32" DbType="int NOT NULL" IsPrimaryKey="true" CanBeNull="false" />
      <Association Name="Child_ParentChild" Member="Child" Storage="_child" ThisKey="ChildId" Type="Child" IsForeignKey="true" DeleteOnNull="false" />
      <Association Name="Parent_ParentChild" Member="Parent" Storage="_parent" ThisKey="ParentId" Type="Parent" IsForeignKey="true" DeleteOnNull="true" />
    </Type>
  </Table>

This is explained here; http://blogs.msdn.com/b/bethmassi/archive/2007/10/02/linq-to-sql-and-one-to-many-relationships.aspx