Nhibernate 多对多 延迟加载无效

有3张表 Part表 Ques表 Part_Ques中间表  
现在在Part表中对Ques配置了many-to-many,并且希望它延迟加载,也就是我在只读取partTitle的时候不要加载Ques,因为Ques表很大,查询很慢.
可是在下面的配置过程中发现Lazy="true"并没有如我所愿.
系统是正常的,因为在配置Exam_Part的关系的时候,Part可以延迟加载,可能是因为他们的关系是one-to-many吧~~ 这个many-to-many就一直不能延迟加载
这个是Part的配置
<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"
   assembly="RMSPExam.Domain"
   namespace="RMSPExam.Domain.Entities.PaperEntities">
    <class name="PaperPart" table ="T_Paper_Parts">
        <id name ="ID" column="ID" type="string" length="50">
            <generator class="uuid.hex"/>
        </id>
        <property name="PartNo" column="Part_No" type="string"/>
        <property name="PartTitle" column="Part_Title" type="string" length="2000"/>
        <bag name="PaperQuestions" lazy="true" table="T_PaperPart_Ques" inverse="true">
            <key column="Part_ID"/>
            <many-to-many column="Ques_ID" class="RMSPExam.Domain.Entities.PaperEntities.PaperQuestion"/>
        </bag >
    </class>
</hibernate-mapping>
Ques配置文件如下,
<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"
   assembly="RMSPExam.Domain"
   namespace="RMSPExam.Domain.Entities.PaperEntities">
    <class name="PaperQuestion" table ="T_Paper_Ques">
        <id name ="ID" column="ID" type="string" length="50">
            <generator class="uuid.hex"/>
        </id>
        <property name="QuestionContent" column="Ques_Content" type="binary"/>
        <join table="T_PaperPart_Ques" fetch="join">
            <key column="Ques_ID"/>
            <many-to-one name="PaperPart" column="Part_ID" class="RMSPExam.Domain.Entities.PaperEntities.PaperPart" lazy="proxy"/>
        </join>
    </class>
</hibernate-mapping>