I don't think this behavior has changed significantly. The key issue is that they seem to have correctly identified that they wanted to prefetch a single task, but they didn't recognize that this setting is the count of un-ACK'ed tasks. If you ACK upon receipt (as most consumers do by default), then you're really prefetching two tasks - one that's being processed, and one that's waiting to be processed. If you ACK late, you get the behavior that TFA seems to want. I've seen this misconfiguration a number of times.