A dash makes the terms into a phrase (ie. they must occur adjacent and in order). To fully resolve the query without post-processing (which can take time and is thus generally disabled), a full Metamorph inverted index is needed.
Such an inverted index is normally what Webinator produces for the main search indexes. However, other indexes may not be inverted. What was the full query given? Was this a main text search or something else? Were any indexes created "by hand" in the scripts?
You may also want to consider adding the - to the index expression (addexp), and making the hyphenphrase setting 0 to allow searches for hyphenated terms.
