The difference between totalHits and scoreDocs.length of TopDocs

TopDocs hits = searcher.search(query, N);
hits.totalHits is not equal to hits.scoreDocs.length in lucene whose version is 4.3.0
when I write the fllowing codes:
for (int i = 0; i < hits.totalHits; i++)

{ int id = hits.scoreDocs[i].doc; //... }

It may throw ArrayIndexOutOfBoundsException, but in version 4.0.0, the value of hits.totalHits and the value of hits.scoreDocs.length are qual!
And I think they should be qual!
Thank you!