This is on topic, really, just bear with me for a sec...
The only reason Google would run it at 4 months is to punish us.
I don't think they think like that. I think they think in terms of information theory.
Google is trying to perform measurements/experiments on a system with a lot of feedback. Every signal they send out into the system causes webmasters to react, so a lot of what Google ends up seeing is sort of a reflection of their own signal.
They regard this as a very frustrating problem. They've stated many times that they wish we would all just ignore them. Google wants to be the silent eavesdropper and listen in on the conversation in the room, but that's very difficult because the echo of their own voice is so loud.
We say "but Google, we're just trying to give you what you want" and their reply is always "don't try to give us what we want, try to give your users what they want." Google wants us to ignore their signal and concentrate on the signal coming from our users.
They've also stated that they are aware that if we were to figure out exactly how Panda works we could game it.
One logical countermeasure on their part would be to deliberately introduce noise into the signal they send out into the system (via the SERPS) in order to mask the signal. Think of it as being similar to noise-cancellation technology. They could try to cancel out the effect of their own signal, fuzzing out the echoes of their own voice so that the underlying signal they are trying to measure stands out more clearly.
One way to do that would be to build a time-delay into their response to any changes we make. Another would be to introduce a certain amount of randomness around any rollout of updates, so that the signal sent by the update is harder for us to read.
So is this another Panda rollout? My suggestion is that it may not actually be possible to tell, from our perspective, because of noise in the system introduced deliberately by Google.
They're tired of us gaming them. They're gaming us for a change.
Given that Google is way better at information theory than we are, and that they have access to many orders of magnitude more data, this is probably a losing game from our perspective. For most of us the logical counter-move is probably capitulation.
"Yes there are two paths you can go by, but in the long run; There's still time to change the road you're on (I hope so)." --Stairway