File system crawl with HSQLDB aborts with a constraint error

While running two jobs with overlapping files with HSQLDB, I got this error on the second job that aborted it:

Error: integrity constraint violation: unique constraint or index violation; SYS_PK_10041 table: INGESTSTATUS

The complete exception is here:

ERROR 2011-08-31 21:07:06,029 (Worker thread '34') - Exception tossed: integrity constraint violation: unique constraint or index violation; SYS_PK_10041 table: INGESTSTATUS
org.apache.manifoldcf.core.interfaces.ManifoldCFException: integrity constraint violation: unique constraint or index violation; SYS_PK_10041 table: INGESTSTATUS
at org.apache.manifoldcf.core.database.DBInterfaceHSQLDB.reinterpretException(DBInterfaceHSQLDB.java:587)
at org.apache.manifoldcf.core.database.DBInterfaceHSQLDB.performModification(DBInterfaceHSQLDB.java:607)
at org.apache.manifoldcf.core.database.DBInterfaceHSQLDB.performUpdate(DBInterfaceHSQLDB.java:242)
at org.apache.manifoldcf.core.database.BaseTable.performUpdate(BaseTable.java:88)
at org.apache.manifoldcf.agents.incrementalingest.IncrementalIngester.updateRowIds(IncrementalIngester.java:628)
at org.apache.manifoldcf.agents.incrementalingest.IncrementalIngester.documentCheckMultiple(IncrementalIngester.java:588)
at org.apache.manifoldcf.crawler.system.WorkerThread.run(WorkerThread.java:653)
Caused by: java.sql.SQLException: integrity constraint violation: unique constraint or index violation; SYS_PK_10041 table: INGESTSTATUS
at org.hsqldb.jdbc.Util.sqlException(Util.java:255)
at org.hsqldb.jdbc.JDBCPreparedStatement.fetchResult(JDBCPreparedStatement.java:4659)
at org.hsqldb.jdbc.JDBCPreparedStatement.executeUpdate(JDBCPreparedStatement.java:311)
at org.apache.manifoldcf.core.database.Database.execute(Database.java:606)
at org.apache.manifoldcf.core.database.Database$ExecuteQueryThread.run(Database.java:421)
Caused by: org.hsqldb.HsqlException: integrity constraint violation: unique constraint or index violation; SYS_PK_10041 table: INGESTSTATUS
at org.hsqldb.error.Error.error(Error.java:134)
at org.hsqldb.Constraint.getException(Constraint.java:914)
at org.hsqldb.index.IndexAVL.insert(IndexAVL.java:731)
at org.hsqldb.persist.RowStoreAVL.indexRow(RowStoreAVL.java:171)
at org.hsqldb.persist.RowStoreAVLDisk.indexRow(RowStoreAVLDisk.java:169)
at org.hsqldb.TransactionManagerMVCC.addInsertAction(TransactionManagerMVCC.java:401)
at org.hsqldb.Session.addInsertAction(Session.java:434)
at org.hsqldb.Table.insertSingleRow(Table.java:2553)
at org.hsqldb.StatementDML.update(StatementDML.java:1032)
at org.hsqldb.StatementDML.executeUpdateStatement(StatementDML.java:541)
at org.hsqldb.StatementDML.getResult(StatementDML.java:196)
at org.hsqldb.StatementDMQL.execute(StatementDMQL.java:190)
at org.hsqldb.Session.executeCompiledStatement(Session.java:1340)
at org.hsqldb.Session.execute(Session.java:993)
at org.hsqldb.jdbc.JDBCPreparedStatement.fetchResult(JDBCPreparedStatement.java:4651)