Recently there was a start of a discussion regarding singleton cache stores and how they behave.  Interestingly according to our documentation [1] and verification code [2] a singleton store cannot be used with a shared cache store.  This makes no sense to me as this means you would have a single point of failure for your data.  And also as Dan pointed out [3] there is no Singleton cache loader to make sure all the loads are from the coordinator either, which means you could have a read that returns null despite it being in the store/loader.