Full text search oddity

I have configured Price Tapestry to use fulltext search in Boolean mode. I have fulltext indexes on both product name and product name + description. Everything is working beautifully, with the exception of a handful of search words which do not show up at all. Examples are 'Krups' and 'Elemaris'. I have downloaded the fulltext indexes and can see that these terms exist in both indexes. I am certain that they do not exceed the 50% rule. Any ideas why they are not showing up?