SOLR "OR" Search Returns All Nodes

Hello,
I'm curious if anyone knows why SOLR returns all nodes on an "OR" search. Or perhaps I'm the only one experiencing this? I'm guessing it's not a drupal-related thing, but I had to ask, as it's making the module quite unusable. Note that this is drupal 5.

For example, if I search for "SOLR", I get a resultset that is a subset of all my nodes, as one would expect. However, if I search for "SOLR OR monkeys" (no quotes, of course), I am returned the entirety of the site's nodes. As you might guess, this includes posts with neither term!

Thanks.