I'll take a quick stab at it. What analyzer are you using with the query? In the search page of Luke, near the upper right there's the "Analyzer to use for query parsing:" box. You might try the WhitespaceAnalyzer, since that shouldn't do anything "interesting". Also, below the search box on the search page, you can get a lot of information from the "update" and "explain structure" buttons.
These make a LOT of lucene's behavior clearer. Finally, watch out for case. Lucene's comparisons are often case-sensitive..... Best Erick
