The Sampler code will mark itself as done once it has populated "limit" number of documents:
if (numDocs >= _options.maxDocsToSample || numBytes >= _options.maxBytesToSample) {
done = true;
break;
}
However, this logic does not take into account how many documents have actually be returned to the client. 

This problem can be reproduced with a batch size of 3 and a limit of 5.