I have a class structure like the following

class Container
{
    public virtual int Id { get; set; }
    public IList<Base> Bases { get; set; }
}

class Base
{
    public virtual int Id { get; set; }
    public virtual string Name { get; set; }
}

class EnemyBase : Base
{
    public virtual int EstimatedSize { get; set; }
}

class FriendlyBase : Base
{
    public virtual int ActualSize { get; set; }
}

Now when I ask the session for a particular Container it normally gives me the concrete EnemyBase and FriendlyBase objects in the Bases collection. I can then (if I so choose) cast them to their concrete types and do something specific with them.

However, sometime I get a proxy of the "Base" class which is not castable to the concrete types. The same method is used both times with the only exception being that in the case that I get proxies I have added some related entities to the session (think the friendly base having a collection of people or something like that).

Is there any way I can prevent it from doing the proxy creating and why would it choose to do this in some scenarios?

UPDATE

The mappings are generated with the automap feature of fluentnhibernate but look something like this when exported

<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" default-access="property" auto-import="true" default-cascade="none" default-lazy="true">
  <class xmlns="urn:nhibernate-mapping-2.2" mutable="true" name="Base" table="`Base`">
    <id name="Id" type="System.Int32, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089">
      <column name="Id" />
      <generator class="MyIdGenerator" />
    </id>
    <property name="Name" type="String">
      <column name="Name" />
    </property>

    <joined-subclass name="EnemyBase">
      <key>
        <column name="Id" />
      </key>
      <property name="EstimatedSize" type="Int">
        <column name="EstimatedSize" />
      </property>

    </joined-subclass>
    <joined-subclass name="FriendlyBase">
      <key>
        <column name="Id" />
      </key>
      <property name="ActualSize" type="Int">
        <column name="ActualSize" />
      </property>

    </joined-subclass>
  </class>
</hibernate-mapping>

<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" default-access="property" auto-import="true" default-cascade="none" default-lazy="true">
  <class xmlns="urn:nhibernate-mapping-2.2" mutable="true" name="Container" table="`Container`">
    <id name="Id" type="System.Int32, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089">
      <column name="Id" />
      <generator class="MyIdGenerator" />
    </id>
    <bag cascade="all-delete-orphan" inverse="true" lazy="false" name="Bases" mutable="true">
      <key>
        <column name="ContainerId" />
      </key>
      <one-to-many class="Base" />
    </bag>  
  </class>
</hibernate-mapping>