The method keySet() of remote client fails (hangs until transport times out) on distributed caches with indexing. This is due to a ClassCastException in the map-reduce task that collects the keys accross the cluster. The task expects the cached value to by byte[], which is not the case if protobuf marshalling is used (because the byte[] value is wrapped by ProtobufValueWrapper). The value is never used by the task, so avoiding the unnecessary casting also avoids this issue.