With most sites I would have never noticed such an occurrence because they are too large but since this site is has only a handful pages these listings jumped off the page at me. Doing an allintitle search for that page title returns only one result. That is what leads me to believe this is a site command bug.
I also noticed the caches are different. The smaller file listing was from an earlier date and the larger one is newer. There are differences in the two pages that are cached but not by much. If nothing else, this tells me Google stores more than one version of a pages cache. Anyone care to take bets on whether they keep all versions forever?
Can anyone else duplicate this on another site?
Disclaimer: I am associated with the site in question.
Update: Turns out the filenames where different by a single dash and WordPress was redirecting the old version to new version. So no bug beyond the 1-2 of 260 mentioned in the first paragraph. Sorry for the confusion.