Interesting, as the majority of these bearings for various engine suppliers are actually mad eby the same company in the same factories on the same machines. Without giving too much away I have been told by someone who works for his manufacturer that the bearings and cases are made in very much the same way, with the same materials to the same tollerances so it is unlikely that if it was a manufacturing fault it would onl affect the renault bearings.
It is more likely a design fault in the assembled unit. They have said that this is because of cooling issues, therefore it would stand to reason that the renault unit when finally assembled has a flaw in the design that allows the casing and bearings to expand at different rates according to the tempratures, this would either cause sticking (if the bearing expanded faster than the casing) which would cause wear and therefore movement when the unit cooled down a little causing further damage and failure, or excessive movement (the casing expanding faster than the bearing) which would cause almost instantaneous damage to the whole unit causing a fast fail.
I can make an informed guess that when these units have been tested (as Renault say they do) they have been done in a lab with cooling provided artificially so the tests may not have found that fatal temperature which causes this issue. In order o find the problem they need to test without cooling and monitor the temps carefully, see the expansion and contraction of each component in the unit (may even be the spindle expanding putting pressure on the bearing) to find their flaw, but this is not a quick process unless you monitor the temps in the race environment to find the proper ranges you need to test against...
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