Hibernate version:3.1

Mapping documents:

<class name="SyndFeedImpl" table="synd_feed">
<id name="uri" column="feed_uri">
<generator class="assigned"/>
</id>

<property name="title" />
..
<bag name="entries" table="feed_entries" cascade="save-update" >
<key column="feed_uri" />
<many-to-many unique="true" column="entry_uri" class="com.sun.syndication.feed.synd.SyndEntryImpl" />
</bag>
</class>


Is there any way to stop rows from the feed_entries table being deleted when the associated object are no longer connected to the SyndFeed? I've tried various cascade options but I can't get it to work.