John Graham-Cumming, the very clever computer scientist who has been replicating CRUTEM thinks he and one of his commenters have found an error in CRUTEM, the land temperature index created by Phil Jones at CRU which forms part of the HADCRUT global temperature index.
I have no idea why the correction given in this blog post by Ilya and I works: perhaps it indicates a genuine bug in the software used to generate CRUTEM3, perhaps it means Ilya and I have failed to understand something, or perhaps it indicates a missing explanation from Brohan et al. I also don't understand why when there are less than 30 years of data the number 30 appears to still be used.
If these are bugs then it indicates that CRUTEM3 will need to be reissued because the error ranges will be all wrong.
John is not a "jump up and down and shout fraud!" kind of guy. He is very careful and very cautious, as you can probably tell from the way he announces his findings.
Those of a mathematical bent might like to take a look and check what he's done.