Lucene returns the same document multiple times

It seems that when a page is modified it is added to lucene's index without deleting the old information in the index.

This causes lucene to have the same page in its index multiple times and thus return multiple instances of the same page.

The lucene FAQ mentions using IndexReader.deleteDocument(docNum) or IndexReader.deleteDocuments(term) if there is a field that holds a unique ID string for the document.