Bidirectional Hibernate collection mapping works in only one direction

Question

My bidirectional collection mapping seems to only work in one direction. One job will have some number of costs. Each cost is associated with one job. The problem is, when I load a job, the costs collection is empty. However, when I load a cost and navigate from it to the job and then check the costs collection, it is properly filled. Can anyone tell me what I'm missing.

Job.hbm.xml

<hibernate-mapping>
    <class name="Job" table="jobs">
        <id column="contract" name="id" type="string">
            <generator class="assigned"/>
        </id>
        <property column="manager" name="manager" type="string"/>
        <property column="startdate" name="startDateAsInt" type="integer"/>
        <property column="orjenddate" name="originalEndDateAsInt" type="integer"/>
        <property column="status" name="status" type="JobStatus"/>
        <many-to-one class="com.fready.pjc.accpac.data.Customer" column="customer" name="customer"/>
        <many-to-one column="ctuniq" name="details" not-null="false" unique="true"/>
        <set name="costs" inverse="true">
            <key column="contract"/>
            <one-to-many class="Cost"/>
        </set>
        <set inverse="true" name="invoiceDetails">
            <key column="contract"/>
            <one-to-many class="InvoiceDetail"/>
        </set>
    </class>
    <query name="allJobs">
    from Job
    </query>
</hibernate-mapping>

Cost.hbm.xml

<hibernate-mapping>
    <class name="Cost" table="costs">
        <composite-id>
            <key-property access="field" column="contract" name="contract"/>
            <key-property access="field" column="transnum" name="transactionNumber"/>
        </composite-id>
        <property access="field" column="costrev" name="costRevenue" type="integer"/>
        <property access="field" column="doctype" name="docType" type="integer"/>
        <property access="field" column="type" name="typeCode" type="integer"/>
        <property column="transdate" name="dateAsInt" type="integer"/>
        <property column="extamthm" name="amount" type="big_decimal"/>
        <many-to-one class="com.fready.pjc.accpac.data.Job" column="contract" insert="false" name="job" update="false" not-null="true"/>
    </class>
    <query name="allCosts">
    from Cost
    </query>
    <query name="byContract">
    from Cost where contract = :contract
    </query>
</hibernate-mapping>