As previously noted, I've also seen this problem and though I thought I'd cleared it up by setting up my own internal caching DNS, it has started happening again just recently.
I think I'm like others. This is a new system. I expected more. Much better. The problem isn't just with the OS. I think it causes other side-effects, which I think are related. When my system goes to sleep or the lid is closed it becomes extremely hot. I'm talking, cooking-on-your-desktop or don't-travel-with-a-Macbook-hot. This is because it is keeping the WiFi and other parts running, while it continuously logs that it is attempting to offload data.
So, with the system a little more than a month old before I discovered it burning hot on my desk on morning, I called Apple and they remotely ran their diagnostics. They noted some odd things, and then the support person literally took a vacation and left me hanging. So, I called and got a new representative. This person asserted "since we've resolved your problem, and this is within expected behavior, is there anything else we can help you with" from the start. I asserted, "NO, we have NOT agreed that the problem is resolved and this is NOT normal behavior, I need a solution." Apple then "offered" that I drive a city away to have some 3rd party technician run diagnostics. I'm not physcially able to get to another city, so I pleaded to no avail for a replacement, being well within warranty and reason.
Point being. There is a shift in responsibility and care at Apple. #1 There is a problem with OS X. #2 If this problem or another is the cause of overheating while a system appears be asleep (Please, do check yours also) this goes far beyond frustration and straight to becoming a potentially dangerous and unsafe product. #3 What happened to honoring product warranties and good customer service.
My interpretation is that they are well aware of the issue and shirking responsibility and stalling.
Six years ago they shipped a system to me with a faulty logic board. I didn't even know it, they told me, and sent a replacement. Six years later, now, they could care less that this system is the tool that enables me to provide for my family and I need it to last to pay for itself and more.