Using version 1.3.1 of the plugin, I see that users are unable to find any results for "ONE-WORD" and "REALLYLONGWORD".
If I remove the hyphen I can find results. When I search the site through Google using the hyphen Google is able to provide results. I realize Google has a lot more resources than a plugin developer but my point is that there IS content that relevant to a hyphenated keyword.
The long word puzzles me. There is plenty of use of it on the site. It's only 12 letters long.
I rebuilt the database and saw no improvement in results.
If I search on the word stem I get similar results to what I would expect to find.
Changing weights on title and copy had no effect.
This appears to be a limitation of the plugin.