Vertical inheritance is broken for subclasses with more than one flattened attribute

In vertical inheritance mapping model, children objects with multiple flattened attributes are handled incorrectly while inserting in database. Cayenne is trying to do as many duplicated INSERTs in children tables as number of flattened attributes in subclass. As example, attached testcase fails with next log messages:

INFO: — transaction started.
Apr 11, 2011 10:42:25 AM org.apache.cayenne.log.CommonsJdbcEventLogger logQuery
INFO: INSERT INTO IV_ROOT (DISCRIMINATOR, ID, NAME) VALUES (?, ?, ?)
Apr 11, 2011 10:42:25 AM org.apache.cayenne.log.CommonsJdbcEventLogger logQueryParameters
INFO: [bind: 1->DISCRIMINATOR:'IvSub2', 2->ID:203, 3->NAME:'XyZX']
Apr 11, 2011 10:42:25 AM org.apache.cayenne.log.CommonsJdbcEventLogger logUpdateCount
INFO: === updated 1 row.
Apr 11, 2011 10:42:25 AM org.apache.cayenne.log.CommonsJdbcEventLogger logQuery
INFO: INSERT INTO IV_SUB2 (ID, SUB2_ATTR, SUB2_NAME) VALUES (?, ?, ?)
Apr 11, 2011 10:42:25 AM org.apache.cayenne.log.CommonsJdbcEventLogger logQueryParameters
INFO: [bind: 1->ID:203, 2->SUB2_ATTR:NULL, 3->SUB2_NAME:NULL]
Apr 11, 2011 10:42:25 AM org.apache.cayenne.log.CommonsJdbcEventLogger logUpdateCount
INFO: === updated 1 row.
Apr 11, 2011 10:42:25 AM org.apache.cayenne.log.CommonsJdbcEventLogger logQueryParameters
INFO: [bind: 1->ID:203, 2->SUB2_ATTR:NULL, 3->SUB2_NAME:NULL]
Apr 11, 2011 10:42:25 AM org.apache.cayenne.log.CommonsJdbcEventLogger logQueryError
INFO: *** error.
java.sql.SQLException: Unique constraint violation: SYS_IDX_76 in statement [INSERT INTO IV_SUB2 (ID, SUB2_ATTR, SUB2_NAME) VALUES (?, ?, ?)]
at org.hsqldb.jdbc.Util.throwError(Unknown Source)
at org.hsqldb.jdbc.jdbcPreparedStatement.executeUpdate(Unknown Source)
at org.apache.cayenne.access.jdbc.BatchAction.runAsIndividualQueries(BatchAction.java:205)
at org.apache.cayenne.access.jdbc.BatchAction.performAction(BatchAction.java:86)
at org.apache.cayenne.access.DataNodeQueryAction.runQuery(DataNodeQueryAction.java:87)
at org.apache.cayenne.access.DataNode.performQueries(DataNode.java:254)
at org.apache.cayenne.access.DataDomainFlushAction.runQueries(DataDomainFlushAction.java:226)
at org.apache.cayenne.access.DataDomainFlushAction.flush(DataDomainFlushAction.java:144)
at org.apache.cayenne.access.DataDomain.onSyncFlush(DataDomain.java:796)
at org.apache.cayenne.access.DataDomain$2.transform(DataDomain.java:763)
at org.apache.cayenne.access.DataDomain.runInTransaction(DataDomain.java:822)
at org.apache.cayenne.access.DataDomain.onSyncNoFilters(DataDomain.java:760)
at org.apache.cayenne.access.DataDomain$DataDomainSyncFilterChain.onSync(DataDomain.java:966)
at org.apache.cayenne.access.DataDomain.onSync(DataDomain.java:731)
at org.apache.cayenne.access.DataContext.flushToParent(DataContext.java:811)
at org.apache.cayenne.access.DataContext.commitChanges(DataContext.java:750)
at org.apache.cayenne.access.VerticalInheritanceTest.testInsert_Sub2(VerticalInheritanceTest.java:139)
...