My guess is that it's the latter: an equivocal review (perhaps the one referenced by puroresu in Msg#73 -- "the most positive is the one that describes it as just short of being boring") was formerly listed as "fresh" but upon reconsideration is now listed as "rotten".
I read on the Rotten Tomatoes message board a comment that said the review by Joe Utichi of FILMFOCUS did, indeed, change his review from "fresh" to "rotten." I don't even need to watch it to know it is rotten. :-)