I hate to do this, but try ROWID (rather than ROWNUM).
The reason I hate to suggest it is because it is not an absolute indicator for the first 150000 records in the table. You make no mention of how much/often the data changes. You don't even mention the version of IDS that you are using. In fact, are you using IDS or Online or SE?
In any case, the simplest answer is to try Rowid. Good luck.