I've also found that this problem is mainly persistent when Hyper Threading is on. I had it on because I was running some simulations. Now that I turned it off it seems to be ok. Considering HT doesn't add anything performance-wise in Linux I'll leave it off for now and use it only when I run experiments.
The processor seems to revert to correct P states when it is off, although it tend to use the max turbo frequency more often.
