jeez : 1000 ?
the issue may come from the fact that the portal creates a transaction when it insert the objects (in order to ensure atomicity among other things), too many objects could lead to have a processing time larget than the transaction timeout value, leading to an automatic rollback of the transaction.
you could try and increase the default value of the transaction timeout :
1/ edit the file server/default/conf/jboss-service.xml
2/ locate the mbean jboss:service=TransactionManager
3/ increase the attribute TransactionTimeout from 300 to a larger value