The way this happened in the past was that - question a and question b got various votes as duplicates of each other. - question a is closed as a duplicate of b - question b is closed for some non-duplicate reason - the majority votes on b are for duplication and the majority action counts This edge case was [solved by the stack developers](http://meta.stackexchange.com/questions/263331/circular-duplicates-strike-again) writing code that clears the duplication votes on b when a is closed as a duplicate of b but historical closures still exist.