You can see what's happening here by taking it out and looking at the visits_frozen test.  We allow the read/write keydir owner to fold even when the keydir is frozen if -1,-1 is passed to the fold function.  That is the case this is designed to prevent: if you are naughty and insist on iterating even though you are frozen, we won't let you use a snapshot bigger than the one before the pending hash was created so that you can not see mutating entries.  We don't give a shit about this case in Riak, as the write won't ever fold, especially not like this. This merely makes sure that the semantics are what's expected of that existing test.