interface IProblemAssociated;

@Entity
class Problem {  // A
  [...]
  ArrayList<IProblemAssociated> associated = new ArrayList<ProblemAssociated>();
  @ManyToAny(
          metaColumn = @Column( name = "property_type" ), fetch=FetchType.LAZY )
  @AnyMetaDef(
      idType = "long",
      metaType = "string",
      metaValues = {
          @MetaValue( value = "ToolInvocation", targetEntity = ToolInvocation.class ),
          [...]
      }
  )
  @JoinTable( name = "Problem_ProblemAssociated", joinColumns = @JoinColumn( name = "problemAssociated_id" ),
    inverseJoinColumns = @JoinColumn( name = "problem_id" ))
  List<IProblemAssociated> getAssociated() {
    return associated;
  }
}

@Entity
class ToolInvocation {}  //B


IProblemAssociated pa = <a ToolInvocation>;
Query q = s.createQuery("FROM Problem where :pa in elements(associated)");
q.setParameter("pa", pa);
return q.list();  // throws SQLException: Operand should contain 1 column(s)

SELECT problem0_.id           AS id24_,
                      [...]
FROM   problem problem0_
WHERE  ? IN (SELECT associated1_.property_type,
                    associated1_.problem_id
             FROM   problem_problemassociated associated1_
             WHERE  problem0_.id = associated1_.problemassociated_id)