weird problem with loading collections of subclasses

[tuxzilla]

I have a class Listing with two collections reviews and discussions. Both Review and Discussion are subclasses mapped to the same table, distinguished by a discriminator column type. I am using Seam 1.2.1 but the problem is most likely related to the persistence mapping. Here are the mappings:

@Entity
@Name("listing")
public class Listing implements java.io.Serializable {
 ...

 @OneToMany(targetEntity = Review.class, cascade = CascadeType.ALL, fetch = FetchType.LAZY, mappedBy = "listing")
 private Set<Review> reviews = new HashSet<Review>(0);

 @OneToMany(targetEntity = Discussion.class, cascade = CascadeType.ALL, fetch = FetchType.LAZY, mappedBy = "listing")
 private Set<Discussion> discussions = new HashSet<Discussion>(0);

}

and

@Entity
@Name("review")
@DiscriminatorValue("review")
@Indexed(index="review")
public class Review extends com.n2.bo.UserContent implements java.io.Serializable {
 ...
 @ManyToOne(fetch = FetchType.LAZY)
 @JoinColumn(name = "listingId")
 private Listing listing;
}


@Entity
@Name("discussion")
@DiscriminatorValue("discussion")
@Indexed(index="discussion")
public class Discussion extends com.n2.bo.UserContent implements java.io.Serializable {
...
@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "listingId")
 private Listing listing;
}

@Entity
@Table(name = "user_content")
@Name("userContent")
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name = "type",
 discriminatorType = DiscriminatorType.STRING)
public class UserContent implements java.io.Serializable {
...
}

The problem I have is that we I load either reviews or discussions of a listing, both reviews and discussions are loaded into one collection, without checking for discriminator value. I verified this with sql statement there was no where type='review' or where type='discussion' clause. Any idea why?

Thanks.