I've had a few of these myself. They have been too few for me to open a support case on as it just doesn't come up that often. I've got a feeling that if I open a case, I'm going to hear that it's just a matter of too many workflow processes getting concurrent writes and one out of a couple thousand has a hiccup.
Still, you should probably open a support case and report back. I, for one, would be very interested in the results/answer.