Paul, my wild, wild guess is that some regression stress tests failed a week or two ago, and it's likely going to be root-caused as an electrical issue. If so, they'll either introduce some microcode patch workaround (best case), some board rework (not-so-good case), or a new stepping of the processor (worst case) in order to remedy the problem. Maybe even a software workaround could be introduced, who knows ...
Tenchu